Method for inspecting substrate, substrate inspecting system and electron beam apparatus

ABSTRACT

The present invention relates to a substrate inspection apparatus for inspecting a pattern formed on a substrate by irradiating a charged particle beam onto the substrate. The substrate inspection apparatus comprises: an electron beam apparatus including a charged particle beam source for emitting a charged particle beam, a primary optical system for irradiating the charged particle beam onto the substrate, a secondary optical system into which a secondary charged particle beam is introduced, the secondary charged particle beam being emitted from the substrate by an irradiation of the charged particle beam, a detection system for detecting the secondary charged particle beam introduced into said secondary optical system and outputting as an electric signal, and a process control system for processing and evaluating the electric signal; a stage unit for holding the substrate and moving the substrate relatively to said electron beam apparatus; a working chamber capable of shielding at least an upper region of the stage unit form outside to control under desired atmosphere; and a substrate load-unload mechanism for transferring the substrate into or out of the stage.

BACKGROUND OF THE INVENTION

In the field of semiconductor processes, the design rule is going intoan age of 100 nm and the production form is on a transition from a massproduction with a few models representative of a DRAM into a small-lotproduction with a variety of models such as a SOC (Silicon on chip).This results in an increase of a number of processes, and an improvementin an yield for each process must be essential, which makes moreimportant an inspection for a defect possibly occurring in each process.The present invention relates to a substrate inspection method forinspecting a substrate such as a wafer after respective processes in thesemiconductor process by using an electron beam, a substrate inspectionapparatus to be used therefor and an electron beam apparatus for theinspection apparatus, and a device manufacturing method using the samemethod and apparatuses.

In conjunction with a high integration of semiconductor device and amicro-fabrication of pattern thereof, an inspection apparatus withhigher resolution and throughput has been desired. In order to inspect awafer substrate of 100 nm design rule for any defects, a resolution insize equal to or finer than 100 nm is required, and the increased numberof processes resulting from a high integration of the device has calledfor an increase in the amount of inspection, which consequently requireshigher throughput. In addition, as a multilayer fabrication of thedevice has been progressed, the apparatus has been further required tohave a function for detecting a contact failure in a via forinterconnecting a wiring between layers (i.e., an electrical defect). Inthe current trend, an inspection apparatus of optical method has beentypically used, but it is expected that an inspection apparatus using anelectron beam may soon be of mainstream, substituting for the inspectionapparatus of optical method in the viewpoint of resolution and ofinspection for contact malfunction. The inspection apparatus of electronbeam method, however, has a weak point in that the inspection apparatusof electron beam method is inferior to the inspection apparatus ofoptical method in the throughput.

Accordingly, an apparatus having higher resolution and throughput andbeing capable of detecting the electrical defects has been desired to bedeveloped. It has been known that the resolution in the inspectionapparatus of optical method is limited to ½ of the wavelength of thelight to be used, and it is about 0.2 μm for an exemplary case of avisible light having put to practical use.

On the other hand, in the method using an electron beam, typically ascanning electron beam method (SEM method) has been put to practice,wherein the resolution thereof is 0.1 μm and the inspection time is 8hours per wafer (20 cm wafer). The electron beam method has adistinctive feature that it is able to inspect for any electricaldefects (breaking of wire in the wirings, bad continuity, bad continuityof via). However, the inspection speed thereof is very low, and so thedevelopment of an inspection apparatus with higher inspection speed hasbeen expected.

Generally, since an inspection apparatus is expensive and a throughputthereof is rather lower as compared to other processing apparatuses,therefore the inspection apparatus has been used after an importantprocess, for example, after the process of etching, film deposition, CMP(Chemical-mechanical polishing) planarization or the like.

The inspection apparatus of scanning electron microscope (SEM) using anelectron beam will now be described. In the inspection apparatus of SEMmethod, the electron beam is focused to be narrower (the diameter ofthis beam corresponds to the resolution thereof) and this narrowed beamis used to scan a sample so as to irradiate it linearly. On the otherhand, moving a stage in the direction normal to the scanning directionallows an observation region to be irradiated by the electron beam as aplane area. The scanning width of the electron beam is typically some100 μm. Secondary electrons emitted from the sample by the irradiationof said focused and narrowed electron beam (referred to as a primaryelectron beam) are detected by a detector (a scintillator plus PMT(i.e., photo multiplier tube) or a detector of semiconductor type (i.e.,a PIN diode type) or the like). A coordinate for an irradiated locationand an amount of the secondary electrons (signal intensity) are combinedand formed into an image, which is stored in a storage or displayed on aCRT (a cathode ray tube). The above description shows the principle ofthe SEM (scanning electron microscope), and defects in a semiconductorwafer (typically made of Si) in the course of processes may be detectedfrom the image obtained in this method. The inspection speed(corresponding to the throughput) is varied in dependence on an amountof primary electron beam (the current value), a beam diameter, and aspeed of response of the detecting system. The beam diameter of 0.1 μm(which may be considered to be equivalent to the resolution), thecurrent value of 100 nA, and the speed of response of the detector of100 MHz are the currently highest values, and in the case using thosevalues the inspection speed has been evaluated to be about 8 hours forone wafer having the diameter of 20 cm. This inspection rate, which isextremely lower as compared with the case using light (not greater than1/20), has been a big problem (drawback).

On the other hand, as a method for improving the inspection speed or adrawback of the SEM method, new SEM (multi beam SEM) method using aplurality of electron beams and an apparatus therefor have beendisclosed. In this method, though the inspection rate can be improved bya number of the plurality of electron beams, there are other problemsthat since a plurality of primary electron beam is irradiated from anoblique direction and a plurality of secondary electron beam is takenout along an oblique direction from a sample, the detector receives thesecondary electrons emitted from the sample only along the obliquedirection, that a shadow emerges on an image, and further that secondaryelectron signals are mixed together because it is difficult to separaterespective secondary electrons coming from the plurality of electronbeams respectively.

Conventionally, there has been known an evaluation apparatus in which aprimary electron beam emitted from an electron gun is focused to benarrower by a lens system to be irradiated onto a surface of the sample,and then secondary electrons emitted from the sample are detected toevaluate the sample surface such as a line width measurement, inspectionfor the defects thereon or the like. In this kind of evaluationapparatus, the S/N ratio is required to be higher than a predeterminedvalue (for example, 22 to 70). In the case where thermal field emissionelectron gun is used, it is required to detect the secondary electronsin a range of 1,000 to 10,000 for each pixel.

For example, assuming a detection efficiency being 10%, 10⁴ to 10⁵pieces of primary electrons have to be irradiated for each pixel. Whenconverting this value into dose, dose D (Q/cm²) may be represented,assuming the pixel size being 0.1 μm square, as:D=10⁴×1.6×10⁻¹⁹ Q/(0.1×10⁻⁴)²˜10⁵×1.6×10⁻¹⁹ Q/(0.1×10⁻⁴)²=16 μc/c m²˜160μc/c m²

Such dose value as in the range of 16 μc/c m² to 160 μc/c m² is asignificantly large value for the wafer containing a layer of almostcompletely finished transistor, and such a dose value may have anegative effect thereon that, for example, a threshold voltage Vth ofthe transistor may increase.

That is, the conventional evaluation apparatus of semiconductor waferhas to employ large S/N ratio and thus large dose, which means when thedose is increased to irradiate large amount of primary electron beam,the threshold voltage of the transistor on the wafer is increased,eventually resulting in a characteristic of the semiconductor devicebeing damaged during the evaluation of a wafer.

Further, in the prior art, there has been another problem that there mayoccur a location offset between an image of secondary electron beamobtained by irradiating the primary electron beam onto the samplesurface and a reference image prepared beforehand, resulting in adeterioration of accuracy in detecting the defect. This location offsetmay cause a considerably serious problem when an irradiation area of theprimary electron beam has an offset with respect to the wafer, andthereby a part of an inspection pattern drops out of the detecting imageof the secondary electron beam, which cannot be dealt with only by atechnology for optimizing a matching area within the detecting image.This must be a fatal drawback especially in the inspection for a finemicro pattern.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a substrate inspectionmethod capable of inspecting and evaluating a sample with highthroughput and high reliability, and a substrate inspection apparatustherefor and an electron beam apparatus for the inspection apparatus.

Another object of the present invention is to provide a substrateinspection method capable of employing a desired level of S/N ratio of adetection signal of a secondary electron even if a dose of a primarycharged particle beam being decreased, and a substrate inspectionapparatus therefor and an electron beam apparatus for the inspectionapparatus.

Still another object of the present invention is to provide a substrateinspection method capable of inspecting for any defects with smallamount of information and of selecting either way of evaluating a largesize of wafer and the like with high throughput or with high accuracy,and a substrate inspection apparatus therefor and an electron beamapparatus for the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection method in which a plurality of charged particle beams may beirradiated at once, and either one of an evaluation with improvedmeasuring accuracy and an evaluation with improved throughput may beselected because of being equipped with a storage section storing a lenscondition or an axial alignment condition of a primary optical systemand a secondary optical system corresponding to a pixel size forscanning the sample, and also to provide a substrate inspectionapparatus therefor and an electron beam apparatus for the inspectionapparatus.

Still another object of the present invention is to provide a substrateinspection method in which independent of an adjustment of the lenscondition of the primary optical system, a focusing condition and amagnifying ratio of the secondary optical system may be adjusted so thata divergence of these values from the design values may be compensatedfor so as to accomplish highly reliable inspection and evaluation, andalso to provide a substrate inspection apparatus therefor and anelectron beam apparatus for the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection apparatus in which an angular aperture may be adjustedindependently between the primary and the secondary optical systems tominimize a number of optical components which cannot be axially alignedand the lens condition may be adjusted in both optical systems, and alsoto provide an electron beam apparatus for the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection method in which in a pattern forming surface of the sample,an area with many defects expected to occur therein and an area withwide variation of evaluation values expected therein are selected so asto irradiate the electron beam or the light thereon to evaluate suchareas with priority, thereby promoting a quick evaluation, and also toprovide a substrate inspection apparatus therefor and an electron beamapparatus for the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection apparatus comprising at least one of a laser reflector mirrorhaving a stiffness as high as possible without any necessity for using athick base body and another laser reflector mirror capable of removingrecesses on a mirror surface possibly caused by voids and at the sametime retaining a highly accurate flatness of the mirror surface, andalso to provide an electron beam apparatus for the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection method in which a killer defect can be discriminated from anon-killer defect even if a minimum line width being 0.1 μm or less, andin addition, an inspection time can be reduced as compared with the caseof the defect inspection apparatus using the SEM, and also to provide asubstrate inspection apparatus therefor and an electron beam apparatusfor the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection method in which an accurate measuring equipment such as alaser interferometer is installed in a stage position and thereby aprecise inspection may be accomplished even in the case where ameasurement is performed under unstable temperature condition or arelative vibration exists between an optical system of an electron beamapparatus and a sample chamber or a stage, and also to provide asubstrate inspection apparatus therefor and an electron beam apparatusfor the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection method in which a single inspection apparatus has a pluralityof functions so that the inspection and the evaluation of the sample maybe performed with small number of apparatuses, thereby reducing a ratioof a foot print occupied by the inspection apparatuses in a clean roomof a semiconductor manufacturing equipment, and also to provide asubstrate inspection apparatus therefor and an electron beam apparatusfor the inspection apparatus.

Still another object of the present invention is to provide a substrateinspection apparatus which is provided with a non-contact supportingmechanism by means of a hydrostatic bearing and a vacuum sealingmechanism by means of differential pumping so that a pressure differencemay be generated between a charged particle beam irradiating region anda hydrostatic bearing support section and a gas desorbed from a surfaceof component facing to the hydrostatic bearing may be reduced, and alsoto provide an electron beam apparatus for the inspection apparatus.

Still another object of the present invention is to provide asemiconductor device manufacturing method in which such a substrateinspection method, a substrate inspection apparatus and a chargedparticle beam apparatus for the inspection apparatus as described aboveare used in the semiconductor device manufacturing process to perform adefect inspection and an evaluation of the sample, thereby improving ayield of device product and preventing any defective products from beingdelivered.

It is to be noted that in the present application, a term “inspection”is used to mean not only an detection of malfunction state such asdefect but also an evaluation of a detected result.

A substrate inspection method according to a first invention of thepresent application comprises the steps of:

(1) emitting a primary charged particle beam from a charged particlebeam source;

(2) irradiating said generated primary charged particle beam onto asubstrate through a primary optical system;

(3) introducing a secondary charged particle beam into a secondaryoptical system, said secondary charged particle beam being emitted fromsaid substrate by said irradiation of said primary charged particlebeam;

(4) detecting said secondary charged particle beam having beenintroduced into said secondary optical system and converting saiddetected secondary charged particle beam into an electric signal; and

(5) processing said electric signal to evaluate said substrate.

In an embodiment of said substrate inspection method, said chargedparticle beam source may be actuated in a space charge limited region,so that the primary charged particle beam emitted from said chargedparticle beam source may be irradiated onto a multi aperture platehaving a plurality of apertures of said primary optical system, andthereby the plurality of charged particle beams having passed throughsaid plurality of apertures may be formed into an image on the substratesurface. Further, said charged particle beam source may be actuated inthe space charge limited region, and said charged particle beam sourcemay emit said primary charged particle beam from a plurality of electronemission region on a circle corresponding to said plurality of aperturesof the multi aperture plate of the primary optical system.

Further, in another embodiment of said substrate inspection method, saidsubstrate inspection method may further comprise a step (6) in whichsaid detection system detects the secondary charged particle beamemitted from a plurality of regions on said substrate to obtain aplurality of sub-image data, and a step (7) for re-arranging saiddetected plurality of sub-image data to generate an image data of theinspection region on the substrate, and may further comprise a step (8)for storing in advance a reference image data with respect to thesubstrate to be evaluated, and a step (9) for evaluating the substrateby comparing said image data generated by an image processor with saidstored reference image data.

Further, in still another embodiment of said substrate inspectionmethod, said substrate may be controlled so as to continuously move inthe Y-axis direction; respective charged particle beam are driven tosimultaneously scan in the X-axis direction such that irradiation spotsof a plurality of primary charged particle beams on the substrate arearranged with equal spacing therebetween in the X-axis direction andrespective scanning regions may partially be superimposed with eachother in the X-axis direction; and while comparing the sub-image data,the X and the Y coordinates of respective charged particle beams aretaken into account thereby inspecting the surface of the substrate.Further, in said substrate inspection method, a lens condition or anaxial alignment condition of said primary and said secondary opticalsystems corresponding to the pixel size for scanning and irradiatingsaid substrate may be stored.

Further, in still another embodiment of said substrate inspectionmethod, said substrate inspection method may further comprise the stepsof converting said electric signal into a pattern information andcomparing said pattern information with a reference pattern, wherein aminimum value of distance between respective charged particle beams insaid plurality of charged particle beams may be controlled to be largerthan a value of resolution of said secondary optical system convertedinto a value on the surface of said substrate.

Further, still another embodiment of said substrate inspection methodmay further comprise the steps of converting said electric signalreceived from said detection section into a binary information,converting said binary information into a rectangular patterninformation, and comparing said rectangular pattern information with thereference pattern.

In still another embodiment of the substrate inspection method accordingto said first invention, for generating an image of the substrate andevaluating a pattern formed on said substrate based on said image, saidmethod may further comprise the steps of: storing a reference imagecorresponding to said image of the substrate; reading out said storedreference image; comparing said image of the substrate with saidread-out reference image and detecting different portions between bothimages; and classifying said different portions into such defectsincluding at least short-circuit, disconnection, convex, chipping,pinhole and isolation; wherein for generating said image of thesubstrate, said method may further comprise the steps of: scanning thesubstrate surface by a plurality of beams each focused to be narrower bythe primary optical system; converging the secondary charged particlebeam from the substrate by an objective lens and further separating saidconverged secondary charged particle beam from the primary opticalsystem by an E×B separator; magnifying an angle formed between an orbitof the secondary charged particle beam from said substrate and anoptical axis by the secondary optical system by using a single stagelens so as to be focused on a multi apertures for detection; anddetecting said focused secondary charged particle beam by a plurality ofdetectors.

Further, in still another embodiment of said substrate inspectionmethod, in a pattern forming surface of said substrate, an area withmany defects being expected to occur therein and an area with widevariation of evaluation values being expected therein may be selected;and the charged particle beam may be irradiated onto these areas toevaluate such areas with priority; wherein: in an evaluation of thepattern forming surface whose whole pattern is formed by dividing saidpattern forming surface into a plurality of areas and forming respectivepattern for each area, said evaluation may be executed by selecting aboundary area between said divided areas; or in an evaluation of thepattern forming surface which is formed by dividing the pattern formingsurface into a plurality of adjacent stripes and forming a pattern foreach stripe by a lithography, said evaluation may be executed byselecting a boundary area between the stripes, a boundary area betweenprimary fields of view or a boundary area between secondary fields ofview of a pattern projection in the lithography.

Further, in still another embodiment of said substrate inspectionmethod, the charged particle beam may be irradiated onto said patternforming surface of the substrate, and said pattern may be evaluatedbased on said secondary charged particle beam, wherein, in the patternforming surface, an area with many defects being expected to occurtherein and an area with wide variation of evaluation values beingexpected therein may be selected, and a central portion of the field ofview of the apparatus used for the present inspection may be located tobe superimposed on the selected areas.

In still another embodiment of the substrate inspection method accordingto said first invention, said method may further comprise the steps of:detecting an abnormal pattern from the image data generated byprocessing said electric signal; and determining whether or not saiddetected abnormal pattern is a killer defect based on a relation thereofwith the predetermined reference pattern; wherein said image processingsection may process a plurality of image data corresponding to saidplurality of secondary charged particle beams simultaneously or inparallel.

Further, in still another embodiment of said substrate inspectionmethod, at least two functions selected from the group consisting of adefect detection of the substrate surface, a defect review of thesubstrate surface, a pattern line width measurement, and a patternpotential measurement may be performed, wherein said defect detection ofthe substrate surface may be performed by comparing the image obtainedby the image signal with the pattern data or by comparing the differentdice with each other; said defect review of the substrate surface may beperformed by observing the image obtained by a scanning of the beam onthe monitor synchronized with a scanning of the primary charged particlebeam on the substrate surface; said pattern line width measurement maybe performed by using a line profile image of the secondary chargedparticle beam obtained when the primary charged particle beam scan thesubstrate surface in a short side direction of the pattern; and saidpattern potential measurement may be performed by applying a negativepotential to an electrode disposed in the nearest location to thesubstrate surface and thereby selectively driving back the secondarycharged particle beam emitted from the pattern on the substrate surfacehaving a high potential.

Still another embodiment of said substrate inspection method may furthercomprise a step of setting an evaluation condition such that a processedcondition of each substrate should be evaluated within a processing timenecessary for processing one substrate by a processing unit, or suchthat the processed condition of one lot of substrates should beevaluated within the processing time necessary for processing one lot ofsubstrates by the processing unit, wherein said step may furthercomprise a step of setting an evaluation area of the substrate such thatthe processed condition should be evaluated only in a specified area.

In still another embodiment of said substrate inspection methodaccording to the first invention, said inspection method may furthercomprise the steps of: obtaining respective images of a plurality ofregions to be inspected each displaced from others while partiallysuperimposing with each other on said substrate; storing a referenceimage; and comparing said obtained images of the plurality of regions tobe inspected with said stored reference image and thereby determining adefect on said substrate.

In still another embodiment of said substrate inspection method, saidinspection method may further comprise the steps of: performing anirradiation of the primary charged particle beam onto said substratewithin a working chamber controlled to be a desired atmosphere;performing a transfer of said substrate into and out of said workingchamber through a space within a vacuum chamber; applying a potential tosaid substrate within said working chamber; and observing the surface ofsaid substrate and aligning said substrate to an irradiation location ofsaid primary charged particle beam.

A second invention according to the present application provides anelectron beam apparatus in which a primary charged particle beam isirradiated onto a substrate to emit a secondary charged particle beamand said secondary charged particle beam is detected to evaluate thesubstrate, said apparatus comprising:

a charged particle beam source for generating the primary chargedparticle beam;

a primary optical system for irradiating a plurality of said primarycharged particle beams onto said substrate while scanning them relativeto said substrate;

a secondary optical system into which the secondary charged particlebeams emitted from said substrate by the irradiation of said primarycharged particle beams are introduced;

a detection system for detecting the secondary charged particle beamsintroduced into said secondary optical system and converting thedetected secondary charged particle beams into an electric signals; and

a process control system for evaluating the substrate based on saidelectric signal.

A third invention according to the present application provides anelectron beam apparatus in which a primary charged particle beam isirradiated onto a substrate to emit a secondary charged particle beamand said secondary charged particle beam is detected to evaluate thesubstrate, said apparatus comprising:

a charged particle beam source for emitting the primary charged particlebeam;

a primary optical system for irradiating a single beam of said primarycharged particle beam onto said substrate while scanning it relative tosaid substrate;

a secondary optical system into which the secondary charged particlebeam emitted from said substrate by the irradiation of said primarycharged particle beam is introduced;

a detection system for detecting the secondary charged particle beamintroduced into said secondary optical system and converting thedetected secondary charged particle beam into an electric signal; and

a process control system for evaluating the substrate based on saidelectric signal.

In an embodiment of the electron beam apparatus according to the secondinvention, said charged particle beam source may be set to actuatewithin a space charge limited region; a cathode of said charged particlebeam source may be made of monocrystal LaB₆; and the charged particlebeam emitted from the charged particle beam source may be irradiatedonto a multi aperture plate having a plurality of apertures of saidprimary optical system, and the plurality of charged particle beamshaving passed through said plurality of apertures may be formed into animage on a surface of said substrate; or alternatively said chargedparticle beam source may be set to actuate within the space chargelimited region; said primary optical system may comprise a multiaperture plate having a plurality of apertures arranged on a circle; anda plurality of cathode of the charged particle beam source, each made ofLaB₆, may be arranged on a circle so that each electron emission regionthereof may correspond to each of said plurality of apertures of saidmulti aperture plate respectively.

Further, in an embodiment of the electron beam apparatus according tothe second invention, said detection system may detect the secondarycharged particle beam emitted from a plurality of regions of saidsubstrate to obtain a plurality of sub-image data, and said electronbeam apparatus may further comprise an image processor for re-arrangingsaid detected plurality of sub-image data to generate an image data ofthe inspection region on the substrate, wherein, said electron beamapparatus may further comprise a memory for storing in advance areference image data with respect to the substrate to be evaluated, andan evaluator for evaluating the substrate by comparing said image datagenerated by said image processor with said reference image data storedin said memory. In said case, said substrate may be controlled so as tocontinuously move in the Y-axis direction; said primary optical systemmay be configured such that respective charged particle beams are drivento simultaneously scan in the X-axis direction so that irradiation spotsof a plurality of charged particle beams on the substrate are arrangedwith approximately equal spacing therebetween in the X-axis direction,and respective scanning regions may partially be superimposed with eachother in the X-direction; and said image processor is configured suchthat while said sub-image data being re-arranged, the X and the Ycoordinates of respective charged particle beams should be taken intoaccount to generate the image data of the substrate surface.

Further, in another embodiment of the electron beam apparatus accordingto the second invention, said apparatus may further comprise a storagesection for storing a lens condition or an axial alignment condition ofsaid primary and said secondary optical systems corresponding to a pixelsize with which said primary charged particle beams are irradiated ontosaid substrate while scanning them relative to said substrate.

Further, in an embodiment of the electron beam apparatus according tothe third invention, said apparatus may further comprise a storagesection for storing a lens condition or an axial alignment condition ofsaid primary and said secondary optical systems corresponding to a pixelsize with which said primary charged particle beams are irradiated ontosaid substrate while scanning it relative to said substrate.

Further, in another embodiment of the electron beam apparatus accordingto the third invention, said apparatus comprises, said electronicoptical system may further comprise: at least one stage of axiallysymmetric lens comprising an electrode made by processing an insulatingmaterial and applying a metal coating onto a surface thereof; aplurality combinations of said charged particle beam source, saidprimary optical system and said secondary optical system, each of saidcombinations comprising an optical column; and a storage section forstoring a lens condition or an axial alignment condition of said primaryand said secondary optical systems corresponding to a pixel size usedfor scanning said substrate.

Further, in another embodiment of the electron beam apparatus accordingto the second invention, in said apparatus, said process control systemmay comprise a secondary charged particle beam processing section,wherein said secondary charged particle beam processing sectioncomprises a converter for converting said electric signal into a patterninformation, and a comparator for comparing said pattern informationwith the reference pattern, wherein a minimum value of distance betweenrespective charged particle beams in said plurality of charged particlebeams may be controlled to be larger than a value of resolution of saidsecondary optical system converted into a value on the surface of saidsubstrate.

Further, in another embodiment of the electron beam apparatus accordingto the second and the third inventions, in said apparatus, said processcontrol system may comprise said image processing section, wherein saidimage processing section may comprise a converter for converting saidelectric signal received from said detection section into a binaryinformation, a converter for converting said binary information into arectangular pattern information, and a comparator for comparing saidrectangular pattern information with the reference pattern. In thiscase, said primary and said secondary optical systems may beaccommodated in an optical column, wherein said primary optical systemmay comprise, in said optical column, at least one axially symmetriclens made of insulating material with an electrode formed on a surfacethereof by metal coating.

Further, in another embodiment of the electron beam apparatus accordingto the second invention, generating an image of the substrate andevaluating a pattern formed on said substrate based on said image may beperformed by: storing a reference image corresponding to said image ofthe substrate; reading out said stored reference image; comparing saidimage of the substrate with said read-out reference image and detectingdifferent portions between both images; and classifying said differentportions into such defects including at least short-circuit,disconnection, convex, chipping, pinhole and isolation; wherein saidgenerating the image of the substrate is performed by: scanning thesubstrate surface by a plurality of beams each focused to be narrower bythe primary optical system; converging the secondary charged particlebeam from the substrate by an objective lens and further separating saidconverged secondary charged particle beam from the primary opticalsystem by an EXB separator; focusing a secondary charged particle beamimage from said substrate on a multi aperture for detection with anangle formed between a secondary electron orbit and an optical axisbeing magnified, by said secondary optical system using at least onestage of lens; and detecting said focused secondary charged particlebeam by a plurality of detectors; wherein said electron beam apparatusmay further comprise (1) a function for pre-aligning said substrate, (2)a function for registering in advance a recipe for performing aninspection of said substrate, (3) a function for reading out a substratenumber formed on said substrate, (4) a function for reading out a recipecorresponding to said substrate by using said read-out substrate number,(5) a function for performing an inspection based on said read-outrecipe, (6) a function for registering in advance an inspection patternimage for said substrate, (7) a function for reading out and displayingsaid registered inspection pattern image, (8) a function for moving saidsubstrate based on a specification on said inspection pattern image or adirection of said recipe so that said specified or directed inspectionpoint may approach a desired location, (9) a function for registering inadvance a reference image for said specified or directed inspectionpoint, (10) a function for forming said reference image for saidspecified or directed inspection point and positioning said inspectionpoint by comparing an image for positioning said specified or directedinspection point with a reference image for positioning said inspectionpoint, (11) a function for forming an image for inspecting saidpositioned inspection point, (12) a function for storing said referenceimage for inspecting said positioned inspection point, (13) a functionfor displaying said image for inspection and said reference image forinspection, (14) a function for comparing said both images to detectdifferent portions therebetween, (15) a function for classifying saiddifferent portions into such defects including at least short-circuit,disconnection, convex, chipping, pinhole and isolation, (16) a functionfor classifying the size of said respective defects including at leastshort-circuit, disconnection, convex, chipping, pinhole and isolation,(17) a function for irradiating a probe onto said different portions onsaid substrate so as to physically analyze, (18) a function foroverwriting said inspection pattern image with a classification resultof the different portions of said specified or directed inspectionpoint, (19) a function for calculating a defect density of all defectsas well as respective defects classified by type or size for respectivechips, substrates and a specified substrate when said substrate is asubstrate, (20) a function for registering in advance a defectsize-critical rate table for said respective defect types, (21) afunction for calculating a yield for respective chips, substrates and aspecified substrate based on said defect size-critical rate table forsaid respective defect types, (22) a function for registering adifferent portion detection result of said specified inspection point, aclassification result of said different portions, and a calculationresult of said respective defect densities and yields, and (23) afunction for outputting said registered respective inspection resultsand calculation results.

Further, in another embodiment of the electron beam apparatus accordingto the second invention, said primary optical system may comprise aaperture plate for forming said primary charged particle beam into aplurality of beams, and an E×B separator, wherein an aperturedetermining an angular aperture for said primary optical system may bedisposed between said aperture plate and said E×B separator, oralternatively, said primary optical system may further comprise acondenser lens for focusing said primary charged particle beam emittedfrom said charged particle beam source to form a crossover image, andthe apertures for forming said primary charged particle beam into aplurality of beams, wherein said apertures may be disposed between saidcondenser lens and said crossover image, and an numerical aperture forsaid primary optical system may be adjusted by changing a magnifyingratio of said crossover image or adjusted to a design value, oralternatively, said primary optical system may further comprise acondenser lens for focusing said primary charged particle beam emittedfrom said charged particle beam source to form a first crossover image,and a aperture plate for forming said primary charged particle beam intoa plurality of beams, wherein said aperture plate may be disposedbetween said condenser lens and said first crossover image, and saidsecondary optical system may further comprise a condenser lens forfocusing said plurality of secondary charged particle beam to form asecond crossover image.

In another embodiment of the electron beam apparatus according to saidfirst and said second inventions, in a pattern forming surface of saidsubstrate, an area with many defects being expected to occur therein andan area with wide variation of evaluation values being expected thereinmay be selected, and the charged particle beam may be irradiated ontothese areas to evaluate such areas with priority, and in this case, inan evaluation of the pattern forming surface whose whole pattern isformed by dividing said pattern forming surface into a plurality ofareas and forming respective pattern for each area, said evaluation maybe executed by selecting a boundary area between said divided areas, oralternatively, in an evaluation of the pattern forming surface which isformed by dividing said pattern forming surface into a plurality ofadjacent stripes and forming a pattern for each stripe by a lithography,said evaluation may be executed by selecting a boundary area between thestripes, a boundary area between primary fields of view of a patternprojection in the lithography or a boundary area between sub-fields ofview.

In another embodiment of the electron beam apparatus according to saidsecond and said third inventions, the charged particle beam isirradiated onto a pattern forming surface of said substrate, and saidpattern is evaluated based on said secondary charged particle beam,wherein, in said pattern forming surface, an area with many defectsbeing expected to occur therein and an area with wide variation ofevaluation values being expected therein may be selected, and a centralportion of the field of view of the apparatus may be positioned to besuperimposed on said selected areas, or alternatively, said processcontrol unit may comprise a secondary charged particle beam signalprocessing section, a detector for detecting an abnormal pattern from animage data generated in said secondary charged particle beam processingsection and a determining system for determining whether or not saiddetected abnormal pattern is a killer defect based on a relation thereofwith a predetermined reference pattern.

In another embodiment of the electron beam apparatus according to saidfirst and said second inventions, said apparatus may further comprise atleast two functions selected from the group consisting of a defectdetection of a substrate surface, a defect review of the substratesurface, a pattern line width measurement, and a pattern potentialmeasurement. In the electron beam apparatus of this embodiment, saiddefect detection of the substrate surface may be performed by comparingan image obtained by an image signal with a pattern data or by comparingdifferent dice with each other, said defect review of the substratesurface may be performed by observing an image obtained by a scanning ofthe beam on a monitor synchronized with a scanning of the primarycharged particle beam on the substrate surface, said pattern line widthmeasurement may be performed by using a line profile image of thesecondary charged particle beam obtained when the primary chargedparticle beam scans the substrate surface in a short side direction ofthe pattern, and said pattern potential measurement may be performed byapplying a negative potential to an electrode disposed in the nearestlocation to the substrate surface and thereby selectively driving backthe secondary charged particle beam emitted from the pattern on thesubstrate surface having a high potential.

In another embodiment of the electron beam apparatus according to saidsecond and said third inventions, said apparatus may further comprise anevaluation condition setter for setting an evaluation condition suchthat a processed condition of each substrate should be evaluated withina processing time necessary for processing one substrate by a processingunit, or alternatively, said apparatus may further comprise anevaluation condition setter for setting an evaluation condition suchthat a processed condition of one lot of substrates should be evaluatedwithin a processing time necessary for processing one lot of substratesby a processing unit. In this case, said evaluation condition setter maycomprise a setter for setting an evaluation area of the substrate suchthat the processed condition should be evaluated only in a specifiedarea on a substrate surface.

In another embodiment of the electron beam apparatus according to saidsecond and said third inventions, said process control unit may comprisean image obtaining device for obtaining respective images of a pluralityof regions to be inspected each displaced from others while partiallysuperimposing with each other on said substrate, a memory for storing areference image, and a defect determining system for comparing saidimages of the plurality of regions to be inspected obtained by saidimage obtaining device with said reference image stored in said memoryand thereby determining a defect on said substrate.

Further, in another embodiment of the electron beam apparatus accordingto said second and said third inventions, a plurality of optical systemseach including said charged particle beam source, said primary opticalsystem, said secondary optical system and said detection system may bearranged on one substrate to be inspected.

Further, in another embodiment of the electron beam apparatus accordingto said second and said third inventions, said primary optical systemmay comprise an objective lens, wherein an electrostatic lens, whichconfigures said objective lens, may have an inner section made ofceramic material having a low linear expansion coefficient which isintegrally configured with another ceramic material disposed outsidethereof, and a plurality of electrodes may be formed on a surface of theceramic material of said inner section by metal coating, wherein each ofsaid plurality of electrodes may be arranged respectively to be axiallysymmetric.

Further, in another embodiment of the electron beam apparatus accordingto said second and said third inventions, said primary optical systemmay comprise an objective lens, wherein an electrostatic lens, whichconfigures said objective lens, may have an inner section made ofceramic material capable of being machined, which is adhesively fixed toanother ceramic material disposed outside thereof; and a plurality ofelectrodes may be formed on a surface of the ceramic material of saidinner section by metal coating, wherein each of said plurality ofelectrodes may be arranged respectively to be axially symmetric.

A fourth invention according to the present application provides asubstrate inspection apparatus for inspecting a pattern formed on asubstrate by irradiating a charged particle beam onto said substrate,said apparatus comprising:

an electron beam apparatus comprising: a charged particle beam sourcefor emitting a charged particle beam; a primary optical system forirradiating said charged particle beam onto said substrate; a secondaryoptical system into which a secondary charged particle beam isintroduced, said secondary charged particle beam being emitted from saidsubstrate by an irradiation of said charged particle beam; a detectionsystem for detecting said secondary charged particle beam introducedinto said secondary optical system and outputting as an electric signal;and a process control system for processing and evaluating said electricsignal;

a stage unit for holding said substrate and moving said substraterelatively to said electron beam apparatus;

a working chamber capable of shielding at least an upper region of saidstage unit form outside to control under desired atmosphere; and

a substrate transfer mechanism for transferring said substrate into orout of said stage.

In an embodiment of the substrate inspection apparatus according to saidfourth invention, said apparatus may further comprise a laserinterferometer for detecting a location of said stage unit, wherein,said primary optical system may comprise an objective lens which isconfigured by an axially symmetric electrostatic lens at least whoseouter section is made of ceramic material having a low linear expansioncoefficient, and a reference mirror of said laser interferometer may bemounted on said outer section of said electrostatic lens.

In another embodiment of said substrate inspection apparatus, saidapparatus may further comprise a laser interferometer which includes alaser reflection mirror mounted at least on said stage unit or formed bypolishing a part of member of said stage unit and is used for measuringa location of said stage by reflecting a laser with said laserreflection mirror, wherein said laser reflection mirror may be formed bya base body made of SiC ceramic.

In another embodiment of the substrate inspection apparatus according tosaid fourth invention, a plurality of optical columns each includingsaid charged particle beam source, said primary optical system, saidsecondary optical system and said detection system may be arrangedtherein in parallel; and a laser interferometer which includes a laserreflection mirror mounted at least on said stage unit or formed bypolishing a part of member of said stage unit and is used for measuringa location of said stage by reflecting a laser with said laserreflection mirror may, wherein said laser reflection mirror may beformed by a base body made of SiC ceramic, and each of said plurality ofoptical columns may comprise at least one stage of axially symmetriclens with an outer diameter processed to be small size by machining aceramic and selectively applying a metal coating on a surface thereof.

In another embodiment of said substrate inspection apparatus, said stageunit may be provided with a non-contact supporting mechanism by means ofa hydrostatic bearing and a vacuum sealing mechanism by means ofdifferential pumping, a divider may be provided for making a conductancesmaller between a region on a surface of said substrate where saidprimary charged particle beam is to be irradiated and a hydrostaticbearing support section of said stage unit, so that a pressuredifference may be generated between said charged particle beamirradiating region and said hydrostatic bearing support section.

In another embodiment of said substrate inspection apparatus, a table ofsaid stage unit may be accommodated in a housing and supported in anon-contact manner by a hydrostatic bearing, said housing accommodatingsaid stage may be vacuumed, and a differential pumping mechanism forevacuating a region on a surface of said substrate where said primarycharged particle beam is to be irradiated may be provided so as tosurround a portion of said electron beam apparatus where said primarycharged particle beam is to be irradiated onto said substrate surface.

Further in another embodiment of said substrate inspection apparatus,said apparatus may further comprise a vibration isolation unit forisolating a vibration from a floor to said vacuum chamber.

Further, in another embodiment of said substrate inspection apparatus,said apparatus may further comprise a potential applying mechanismdisposed in said working chamber for applying a potential to said objectto be inspected, and an alignment control unit for observing a surfaceof said object to be inspected and controlling an alignment thereof inorder to position said object to be inspected with respect to saidelectron optical system.

Further, in another embodiment of said substrate inspection apparatus,said electron beam apparatus may be any electron beam apparatus definedin either of claim 24 to 55.

A fifth invention according to the present application provides asemiconductor device manufacturing method comprising a step ofevaluating a semiconductor substrate in a course of processes or afterhaving been completed by using either of the substrate inspectionmethod, the electron beam apparatus or the substrate inspectionapparatus, described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional elevational view taken along a line A—A ofFIG. 2, illustrating main components of an inspection apparatusaccording to the present invention;

FIG. 2 is a cross-sectional plan view taken along a line B—B of FIG. 1,illustrating the main components of the inspection apparatus shown inFIG. 1 according to the present invention;

FIG. 3 is a cross sectional view of an alternative embodiment of acassette holder;

FIG. 4 is a cross sectional view taken along a line C—C of FIG. 1,illustrating a mini-environment chamber shown in FIG. 1;

FIG. 5 is a cross sectional view taken along a line D—D of FIG. 2,illustrating a loader housing shown in FIG. 1;

FIG. 6 is an enlarged view of a wafer rack, wherein (A) is a sideelevational view and (B) is a cross sectional view taken along a lineE—E of (A);

FIG. 7 shows an alternative embodiment of a main housing support system;

FIG. 8 is a diagram illustrating a general configuration of anelectronic optical system of the inspection apparatus shown in FIG. 1;

FIG. 9 shows a positional relationship between apertures in a multiaperture plate used in an primary optical system of the electron opticalsystem shown in FIG. 8;

FIG. 10 illustrates an electron gun operating condition of the electronoptical system shown in FIG. 8;

FIG. 11 illustrates an ExB separator;

FIG. 12 illustrates a scanning/irradiating method of a primary electronbeam on a wafer;

FIG. 13 is a block diagram illustrating a configuration of an image dataprocessing section shown in FIG. 8;

FIG. 14 illustrates an operation of an image data re-arranging deviceshown in FIG. 13;

FIG. 15 shows a potential applying mechanism;

FIG. 16 illustrates an electron beam calibration mechanism, wherein (A)is a side elevational view and (B) is a plan view;

FIG. 17 is a schematic diagram of an alignment control device for awafer;

FIG. 18 is a block diagram illustrating a flow of inspection algorism;

FIG. 19 is a flow chart illustrating an embodiment of a semiconductordevice manufacturing method according to the present invention;

FIG. 20 is a flow chart illustrating a lithography process, a coreprocess in a wafer processing processes of FIG. 19;

FIG. 21 illustrates an arrangement of optical columns barrels in theelectron beam apparatus;

FIG. 22 illustrates an evaluation region in an alternative embodiment ofthe inspection method;

FIG. 23 is an enlarged view of an area encircled by a circle Cr of FIG.22;

FIG. 24(A) is a diagram for illustrating a pattern line widthinspection, and FIG. 24(B) is a diagram for illustrating a potentialcontrast measurement of a pattern;

FIG. 25 shows another embodiment of a stage unit used in the substrateinspection apparatus according to the present invention, wherein (A) isan elevational view and (B) is a side elevational view;

FIG. 26 is a detailed perspective view of a hydrostatic bearing sectionshown in FIG. 25;

FIG. 27 shows another embodiment of a stage unit and an embodiment ofevacuating system on a tip of the optical column used in the substrateinspection apparatus according to the present invention;

FIG. 28 shows another embodiment of the stage unit and the evacuatingsystem on a tip of the optical column used in the substrate inspectionapparatus according to the present invention;

FIG. 29 shows still another embodiment of the stage unit and theevacuating system on a tip of the optical column used in the substrateinspection apparatus according to the present invention;

FIG. 30 shows still another embodiment of the stage unit and theevacuating system on a tip of the optical column used in the substrateinspection apparatus according to the present invention;

FIG. 31 shows another embodiment of a vacuum chamber and an XY stageused in the substrate inspection apparatus according to the presentinvention;

FIG. 32 shows an example of a differential pumping mechanism installedin the system shown in FIG. 31;

FIG. 33 shows a circulation piping system of gas for the system shown inFIG. 31;

FIG. 34 is a diagram illustrating a general configuration of anotherembodiment of the electron beam apparatus according to the presentinvention;

FIG. 35 is a schematic diagram illustrating a potential distribution ina potential contrast measurement;

FIG. 36 is a diagram illustrating a relation between a pulse potentialapplied to a blanking deflector and an incident beam current onto asample in a potential measurement of high time resolution;

FIG. 37 is a flow chart illustrating an inspection procedure accordingto the present invention;

FIG. 38 is a diagram illustrating a general configuration of stillanother embodiment of the electron beam apparatus according to thepresent invention;

FIG. 39 is a diagram for explaining a wafer inspection method accordingto the present invention, illustrating a pattern defect detection;

FIG. 40 is a diagram illustrating a general configuration of stillanother embodiment of the electron beam apparatus according to thepresent invention;

FIG. 41 is a diagram illustrating an embodiment of a scanning electronbeam apparatus to which a feature of the electron beam apparatus of FIG.40 is applied;

FIG. 42 illustrates an arrangement of the optical systems in theelectron beam apparatus;

FIG. 43 is a diagram illustrating a general configuration of stillanother embodiment of the electron beam apparatus according to thepresent invention;

FIG. 44 illustrates a configuration of an electrostatic lens, whichconfigures an object lens, installed in the electron beam apparatusshown in FIG. 43;

FIG. 45 is a diagram illustrating an embodiment of a scanning electronbeam apparatus to which a feature of the apparatus shown in FIG. 43 isapplied;

FIG. 46 is a block diagram illustrating a preferred manufacturingprocess of a laser reflection mirror shown in FIG. 44;

FIG. 47 is a diagram illustrating a general configuration of stillanother embodiment of the electron beam apparatus according to thepresent invention;

FIG. 48 is a diagram illustrating a general configuration of stillanother embodiment of the electron beam apparatus according to thepresent invention;

FIG. 49 illustrates how to discriminate a killer defect from anon-killer defect in an inspection by the electron beam apparatus ofFIG. 48;

FIG. 50 is a diagram illustrating a general configuration of stillanother embodiment of the electron beam apparatus according to thepresent invention;

FIG. 51 illustrates an aperture plate having a plurality of aperturesinstalled in the electron beam apparatus shown in FIG. 50;

FIG. 52 illustrates an example in which is arranged a plurality ofoptical systems each having an integrated electron beam apparatusaccording to the present invention;

FIG. 53 is a diagram illustrating a general configuration of anotherembodiment of the defect inspection apparatus using the electron beamapparatus according to the present invention;

FIG. 54 illustrates an example of a plurality of images to be inspectedobtained by the defect inspection apparatus of FIG. 53 as well as areference image;

FIG. 55 is a flow chart illustrating a flow of a main routine for waferinspection in the defect inspection apparatus of FIG. 53;

FIG. 56 is a flow chart illustrating a detailed flow of a sub-routine ina process for obtaining a plurality of image data to be inspected inFIG. 55;

FIG. 57 is a flow chart illustrating a detailed flow of a sub-routine ina comparison process in FIG. 55; and

FIG. 58 is a conceptual diagram illustrating a plurality of regions tobe inspected, each being displaced from others while partiallysuperimposing with each other on a surface of the semiconductor wafer.

DETAILED DESCRIPTION OF THE INVENTION

There will now be described preferred embodiments of the presentinvention as a substrate inspection apparatus for inspecting a substrateor a wafer as an object to be inspected having a pattern formed on asurface thereof, with reference to the attached drawings.

Referring to FIGS. 1 and 2, main components of a substrate inspectionapparatus 1 according to an embodiment of the present invention is shownby an elevational view and a plan view.

The semiconductor testing apparatus 1 of this embodiment comprises acassette holder 10 for holding cassettes which stores a plurality ofwafers; a mini-environment chamber 20; a main housing 30 which defines aworking chamber; a loader housing 40 disposed between themini-environment chamber 20 and the main housing 30 to define twoloading chambers; a loader 60 for loading a wafer from the cassetteholder 10 onto a stage device 50 disposed in the main housing 30; and anelectro-optical device 70 installed in the vacuum main housing 30. Thesecomponents are arranged in a positional relationship as illustrated inFIGS. 1 and 2. The semiconductor testing apparatus 1 further comprises apre-charge unit 81 disposed in the vacuum main housing 30; a potentialapplying mechanism 83 (see in FIG. 15) for applying a to a wafer; anelectron beam calibration mechanism 85 (see in FIG. 16); and an opticalmicroscope 871 which forms part of an alignment controller 87 foraligning the wafer on the stage device 50.

Cassette Holder

The cassette holder 10 is configured to hold a plurality (two in thisembodiment) of cassettes 14 (for example, closed cassettes such asSMIF,FOUP manufactured by Assist Co.) in which a plurality (for example,25) of wafers are placed side by side in parallel, oriented in thevertical direction. The cassette holder can be arbitrarily selected forinstallation adapted to a particular loading mechanism. Specifically,when a cassette, carried to the cassette holder 10, is automaticallyloaded into the cassette holder 10 by a robot or the like, the cassetteholder 10 having a structure adapted to the automatic loading can beinstalled. When a cassette is manually loaded into the cassette holder10, the cassette holder 10 having an open cassette structure can beinstalled. In this embodiment, the cassette holder 10 is the typeadapted to the automatic cassette loading, and comprises, for example,an up/down table 11, and an elevation mechanism 12 for moving theup/down table 11 up and down. The cassette 14 can be automatically setonto the up/down table 11 in the position indicated by chain lines inFIG. 2. After the setting, the cassette c is automatically rotated tothe position indicated by solid lines in FIG. 2 so that it is directedto the axis of pivotal movement of a first carrier unit within themini-environment chamber 20. In addition, the up/down table 11 is moveddown to the position indicated by chain lines in FIG. 1. In this way,the cassette holder 10 for use in automatic loading, or the cassetteholder 10 for use in manual loading may be both implemented by those inknown structures, so that detailed description on their structures andfunctions are omitted.

As an alternative embodiment for the above described cassette holder 10and cassette 14, such a device 10 a as shown in FIG. 3 may beconsidered. This device 10 a holds a plurality of substrates W with adiameter of 300 mm in a substrate carrier box 15 a with each substratebeing separated from others. This substrate carrier box 15 a has a boxmain body 151 disposed on a stationary table 11 a, and conveys andstores the wafers W horizontally and parallelly with each other as eachcontained in a slot-like pocket (not shown) fixedly mounted in said boxmain body. The box main body 151 a of the substrate carrier box 15 a hasan opening in a side facing to a mini-environment chamber, and saidopening is designed to be selectively opened or closed by a door 152 afor carrying in/out the substrate, said door being provided in a housing22 of the mini-environment chamber. This door 152 a for carrying in/outthe substrate is designed to be opened/closed by an automatic dooropening/closing unit, though not shown. The device 10 a comprises a lidbody 153 a, which is disposed in an opposite side of said opening facingto the mini-environment chamber, for covering another opening throughwhich filters and a fun motor are to be attached or detached, said slotlike pocket (not shown) for holding the substrate, a UPA filter 155 a, achemical filter 156 a, and a fun motor 157 a. In this embodiment also,the wafer W is carried in or out by a first transfer unit 61 of robottype in a loader 60.

It is to be noted that the substrate or the wafer received in thecassette 14 is a wafer to be subjected to an inspection, wherein saidinspection is performed after or in a course of a process for processingthe wafer in the semiconductor manufacturing process. In specific, sucha substrate or a wafer as having been subjected to a film depositionprocess, a CMP process, or an ion implantation process, a wafer with awiring pattern formed thereon or a wafer with a wiring pattern not yetformed thereon is received in the cassette. Since a plurality of wafersis received in the cassette 14 so as to be arranged horizontally andparallelly placing a space therebetween and stacked vertically, an armof the first transfer unit is designed to be movable vertically so thata wafer in any position may be caught by said first transfer unit aswill be described later.

Mini-Environment Chmber

In FIGS. 1, 2 and 4, the mini-environment chamber 20 comprises a housing22 which defines a mini-environment space 21 that is controlled for anatmosphere; a gas circulating device 23 for circulating a gas such asclean air within the mini-environment space 21 for the control; adischarging device 24 for recovering a portion of air supplied into themini-environment space 21 for discharging; and a pre-aligner 25 forroughly aligning a substrate, i.e., a wafer under testing, which isplaced in the mini-environment space 21.

The housing 22 has a top wall 221, a bottom wall 222, and peripheralwall 223 which surrounds four sides of the housing 22 to provide astructure for isolating the mini-environment space 21 from the outside.For controlling the atmosphere in the mini-environment space 21, the gascirculating device 23 comprises a gas supply unit 231 attached to thetop wall 221 within the mini-environment space 21 as illustrated in FIG.4 for cleaning a gas (air in this embodiment) and delivering the cleanedgas downward through one or more gas delivering ports (not shown) inlaminar flow; a recovery duct 232 disposed on the bottom wall 222 withinthe mini-environment space for recovering air which has flown down tothe bottom; and a conduit 233 for connecting the recovery duct 232 tothe gas supply unit 231 for returning recovered air to the gas supplyunit 231. In this embodiment, the gas supply unit 231 takes about 20% ofair to be supplied, from the outside of the housing 22 for cleaning.However, the percentage of gas taken from the outside may be arbitrarilyselected. The gas supply unit 231 comprises an HEPA or ULPA filter in aknown structure for creating cleaned air. The laminar downflow ofcleaned air is mainly supplied such that the air passes a carryingsurface formed by the first carrier unit, later described, disposedwithin the mini-environment space 21 to prevent dust particles, whichcould be produced by the carrier unit, from attaching to the wafer.Therefore, the downflow nozzles need not be positioned near the top wallas illustrated, but is only required to be above the carrying surfaceformed by the carrier unit. In addition, the air need not either besupplied over the entire mini-environment space 21. It should be notedthat an ion wind may be used as cleaned air to ensure the cleanliness asthe case may be. Also, a sensor may be provided within themini-environment space 21 for observing the cleanliness such that theapparatus is shut down when the cleanliness is degraded. An access port225 is formed in a portion of the peripheral wall 223 of the housing 22that is adjacent to the cassette holder 10. A gate valve in a knownstructure may be provided near the access port 225 to shut the accessport 225 from the mini-environment chamber 20. The laminar downflow nearthe wafer may be, for example, at a rate of 0.3 to 0.4 m/sec. The gassupply unit 231 may be disposed outside the mini-environment space 21instead of within the mini-environment space 21.

The discharging device 24 comprises a suction duct 241 disposed at aposition below the wafer carrying surface of the carrier unit and belowthe carrier unit; a blower 242 disposed outside the housing 22; and aconduit 243 for connecting the suction duct 241 to the blower 242. Thedischarging device 24 sucks a gas flowing down around the carrier unitand including dust, which could be produced by the carrier unit, throughthe suction duct 241, and discharges the gas outside the housing 22through the conduits 243, 244 and the blower 242. In this event, the gasmay be emitted into an exhaust pipe (not shown) which is laid to thevicinity of the housing 22.

The aligner 25 disposed within the mini-environment space 21 opticallyor mechanically detects an orientation flat (which refers to a flatportion formed on the outer periphery of a circular wafer) formed on thewafer, or one or more V-shaped notches formed on the outer peripheraledge of the wafer to previously align the position of the wafer in arotating direction about the axis O₁—O₁ at an accuracy of approximately± one degree. The pre-aligner forms part of a mechanism for determiningthe coordinates of an object under testing and is responsible for roughalignment of an object under testing. Since the pre-aligner itself maybe of a known structure, description on its structure and operation isomitted.

Although not shown, a recovery duct for the discharger 24 may also beprovided below the pre-aligner such that air including dust, emittedfrom the pre-aligner, is discharged to the outside.

Main Housing

In FIGS. 1 and 2, the main housing 30, which defines the working chamber31, comprises a housing body 32 that is supported by a housingsupporting device 33 fixed on a vibration isolator 37 disposed on a baseframe 36. The housing supporting device 33 comprises a frame structure331 assembled into a rectangular form. The housing body 32 comprises abottom wall 321 securely fixed on the frame structure 331; a top wall322; and a peripheral wall 323 which is connected to the bottom wall 321and the top wall 322 and surrounds four sides of the housing body 32,and isolates the working chamber 31 from the outside. In thisembodiment, the bottom wall 321 is made of a relatively thick steelplate to prevent distortion due to the weight of equipment carriedthereon such as the stage device. Alternatively, another structure maybe employed. In this embodiment, the housing body 32 and the housingsupporting device 33 are assembled into a rigid construction, and thevibration isolator 37 prevents vibrations from the floor, on which thebase frame 36 is placed, from being transmitted to the rigid structure.A portion of the peripheral wall 323 of the housing body 32 that adjoinsthe loader housing 40, later described, is formed with an access port325 for introducing and removing a wafer.

The vibration isolator 37 may be either of an active type which has anair spring, a magnetic bearing and so on, or a passive type likewisehaving these components. Since any known structure may be employed forthe vibration isolator 37, description on the structure and functions ofthe vibration isolator itself is omitted. The working chamber 31 is heldin a vacuum atmosphere by a vacuum system (not shown) in a knownstructure. A controller 2 for controlling the operation of the overallapparatus is disposed below the base frame 36.

The vacuum system described above is composed of a vacuum pump, a vacuumvalve, a vacuum gauge, a vacuum pipe and the like, though each being notshown, and exhausts to vacuum an electronic optical system, a detectorsection, a working chamber and a loading chamber which will be describedlater, according to a predetermined sequence. In each of those sections,the vacuum valve is controlled so as to accomplish a required vacuumlevel. The vacuum level is regularly monitored, and in the case ofirregularity, an interlock function executes an emergency control suchas an interception of communication between the chambers or between thechamber and the evacuating system by an isolation valve, though notshown, to secure the vacuum level for each section. As for the vacuumpump, a turbo molecular pump may be used for main exhaust, and a drypump of Root type may be used as a roughing vacuum pump. A pressure atan inspection spot (an electron beam irradiating section) or in theworking chamber is practically in a range of 10⁻³ to 10⁻⁵ Pa, preferablyin a range of 10⁻⁴ to 10⁻⁶ Pa as shifted by one digit down.

Loader Housing

In FIGS. 1, 2 and 5, the loader housing 40 comprises a housing body 43which defines a first loading chamber 41 and a second loading chamber42. The housing body 43 comprises a bottom wall 431; a top wall 432; aperipheral wall 433 which surrounds four sides of the housing body 43;and a partition wall 434 for partitioning the first loading chamber 41and the second loading chamber 42 such that both the loading chamberscan be isolated from the outside. The partition wall 434 is formed withan aperture, i.e., an access port 435 for passing a wafer between boththe loading chambers. Also, portions of the peripheral wall 433 thatadjoin the mini-environment chamber 20 and the main housing 30 is formedwith access ports 436 and 437, respectively. The housing body 43 of theloader housing 40 is carried on and supported by the frame structure 331of the housing supporting device 33. This prevents the vibrations of thefloor from being transmitted to the loader housing 40 as well. Theaccess port 436 of the loader housing 40 is in alignment with the accessport 226 of the housing 22 of the mini-environment chamber 20, and agate valve 27 is provided for selectively isolating a interactionbetween the mini-environment space 21 and the first loading chamber 41.The gate valve 27 has a sealing material 271 which surrounds theperipheries of the access ports 226, 436 and is fixed to the side wall433 in close contact therewith; a door 272 for isolating air fromflowing through the access ports in cooperation with the sealingmaterial 271; and an actuator 273 for moving the door 272. Likewise, theaccess port 437 of the loader housing 40 is in alignment with the accessport 325 of the housing body 32, and a gate valve 45 is provided forselectively isolating a intraction between the second loading chamber 42and the working chamber 31 in a hermetic manner. The gate valve 45comprises a sealing material 451 which surrounds the peripheries of theaccess ports 437 and 325 and is fixed to side walls 433 and 323 in closecontact therewith; a door 452 for isolating air from flowing through theaccess ports in cooperation with the sealing material 451; and anactuator 453 for moving the door 452. Further, the aperture formedthrough the partition wall 434 is provided with a gate valve 46 forclosing the aperture with the door 461 to selectively isolating ainteraction between the first and second loading chambers in a hermeticmanner. These gate valve 27, 45, 46 are configured to provide air-tightsealing for the respective chambers when they are in a closed state.Since these gate valve may be implemented by known ones, detaileddescription on their structures and operations is omitted. It should benoted that a method of supporting the housing 22 of the mini-environmentchamber 20 is different from a method of supporting the loader housing40. Therefore, for preventing vibrations from being transmitted from thefloor through the mini-environment chamber 20 to the loader housing 40and the main housing 30, a vibration-absorption damping material may bedisposed between the housing 22 and the loader housing 40 to provideair-tight sealing for the peripheries of the access ports.

Within the first loading chamber 41, a wafer rack 47 is disposed forsupporting a plurality (two in this embodiment) of wafers spaced in thevertical direction and maintained in a horizontal position. Asillustrated in FIG. 6, the wafer rack 47 comprises posts 472 fixed atfour corners of a rectangular substrate 471, spaced from one another, inan upright position. Each of the posts 472 is formed with supportingdevices 473 and 474 in two stages, such that peripheral edges of wafersW are carried on and held by these supporting devices. Then, leadingends of arms of the first and second carrier units, later described, arebrought closer to wafers from adjacent posts and grab the wafers.

The loading chambers 41 and 42 can be controlled for the atmosphere tobe maintained in a high vacuum condition (at a pressure of 10⁻⁵ to 10⁻⁶Pa) by a pumping system (not shown) in a known structure including avacuum pump for the working chamber, not shown. In this event, the firstloading chamber 41 may be held in a low vacuum condition as a low vacuumchamber, while the second loading chamber 42 may be held in a highvacuum condition as a high vacuum chamber, to effectively preventcontamination of wafers. The employment of such a structure allows awafer, which is accommodated in the loading chamber and is nextsubjected to the defect testing, to be carried into the working chamberwithout delay. The employment of such a loading chambers provides for animproved throughput for the defect testing, and the highest possiblevacuum condition around the electron source which is required to be keptin a high vacuum condition, together with the principle of a multi-beamtype electron system, later described.

The first and second loading chambers 41 and 42 are connected to avacuum exhaust pipe and a vent pipe for an inert gas (for example, driedpure nitrogen) (neither of which are shown), respectively. In this way,the atmospheric state within each loading chamber is attained by aninert gas vent (which injects an inert gas to prevent an oxygen gas andso on other than the inert gas from attaching on the surface). Since anapparatus itself for implementing the inert gas vent is known instructure, detailed description thereon is omitted.

In the testing apparatus according to the present invention which usesan electron beam, when representative lanthanum hexaboride (LaB₆) usedas an electron source for an electro-optical system, later described, isonce heated to such a high temperature that causes emission of thermalelectrons, it should not be exposed to oxygen within the limits ofpossibility so as not to shorten the lifetime. The exposure to oxygencan be prevented without fail by carrying out the atmosphere control asmentioned above at a stage before loading a wafer into the workingchamber in which the electron-optical system is disposed.

Stage Device

The stage device 50 comprises a fixed table 51 disposed on the bottomwall 301 of the main housing 30: a Y-table 52 movable in a Y-directionon the fixed table 51 (the direction vertical to the drawing sheet inFIG. 1); an X-table 54 movable in an X-direction on the Y-table 52 (inthe left-to-right direction in FIG. 1); a turntable 56 rotatable on theX-table; and a holder 57 disposed on the turntable 56. A wafer isreleasably held on a wafer carrying surface 571 of the holder 57. Theholder 57 may be of a known structure which is capable of releasablygrabbing a wafer by means of a mechanical or electrostatic chuckfeature. The stage device 50 uses servo motors, encoders and a varietyof sensors (not shown) to operate a plurality of tables as mentionedabove to permit highly accurate alignment of a wafer held on thecarrying surface 571 by the holder 57 in the X-direction, Y-directionand Z-direction (in the up-down direction in FIG. 1) with respect to anelectron beam irradiated from the electro-optical device, and in adirection about the axis normal to the wafer supporting surface (θdirection). The alignment in the Z-direction may be made such that theposition on the carrying surface of the holder, for example, can befinely adjusted in the Z-direction. In this event, a reference positionon the carrying surface is sensed by a position measuring device using alaser of an extremely small diameter (a laser interferometer) to controlthe position by a feedback circuit, not shown. Additionally oralternatively, the position of a notch or an orientation flat of a waferis measured to sense a plane position or a rotational position of thewafer relative to the electron beam to control the position of the waferby rotating the turntable 54 by a stepping motor which can be controlledin extremely small angular increments. In order to maximally preventparticle produced within the working chamber, servo motors 531, 531 andencoders 522, 532 for the stage device 50 are disposed outside the mainhousing 30. Since the stage device 50 may be of a known structure used,for example, in steppers and so on, detailed description on itsstructure and operation is omitted. Likewise, since the laserinterferometer may also be of a known structure, detailed description onits structure and operation is omitted.

It is also possible to establish a basis for signals which are generatedby previously inputting a rotational position, and X-, Y-positions of awafer relative to the electron beam in a signal detecting system or animage processing system, later described. The wafer chucking mechanismprovided in the holder is configured to apply a voltage for chucking awafer to an electrode of an electrostatic chuck, and the alignment ismade by pinning three points on the outer periphery of the wafer(preferably spaced equally in the circumferential direction). The waferchucking mechanism comprises two fixed aligning pins and a push-typeclamp pin. The clamp pin can implement automatic chucking and automaticreleasing, and constitutes a conducting spot for applying the voltage.While in this embodiment, the X-table is defined as a table which ismovable in the left-to-right direction in FIG. 2; and the Y-table as atable which is movable in the up-down direction, a table movable in theleft-to-right direction in FIG. 2 may be defined as the Y-table; and atable movable in the up-down direction as the X-table.

Loader

The loader 60 comprises a robot-type first carrier unit 61 disposedwithin the housing 22 of the mini-environment chamber 20; and arobot-type second carrier unit 63 disposed within the second loadingchamber 42.

The first carrier unit 61 comprises a multi-node arm 612 rotatable aboutan axis O₁—O₁ with respect to an actuator 611. While an arbitrarystructure may be used for the multi-node arm, the multi-node arm in thisembodiment has three parts which are pivotably attached to each other.One part of the arm 612 of the first carrier unit 61, i.e., the firstpart closest to the actuator 611 is attached to a rotatable shaft 613 bya driving mechanism (not shown) of a known structure, disposed withinthe actuator 611. The arm 612 is pivotable about the axis O₁—O₁ by meansof the shaft 613, and radially telescopic as a whole with respect to theaxis O₁—O₁through relative rotations among the parts. At a leading endof the third part of the arm 612 furthest away from the shaft 613, aholding device 616 in a known structure for holding a wafer, such as amechanical chuck or an electrostatic chuck, is disposed. The actuator611 is movable in the vertical direction by an elevating mechanism 615in a known structure.

The first carrier unit 61 extends the arm 612 in either a direction M1or a direction M2 of two cassettes 14 held in the cassette holder 10,and removes a wafer accommodated in a cassette 14 by carrying the waferon the arm or by grabbing the wafer with the chuck (not shown) attachedat the leading end of the arm. Subsequently, the arm is retracted (in aposition as illustrated in FIG. 2), and then rotated to a position atwhich the arm can extend in a direction M3 toward the prealigner 25, andstopped at this position. Then, the arm is again extended to transferthe wafer held on the arm to the prealigner 25. After receiving a waferfrom the prealigner 25, contrary to the foregoing, the arm is furtherrotated and stopped at a position at which it can extend to the secondloading chamber 41 (in the direction M3), and transfers the wafer to awafer rack 47 within the second loading chamber 41. For mechanicallygrabbing a wafer, the wafer should be grabbed on a peripheral region (ina range of approximately 5 mm from the peripheral edge). This is becausethe wafer is formed with device construction (circuit patterns) over theentire surface except for the peripheral region, and grabbing the innerregion would result in failed or defective devices.

The second carrier unit 63 is basically identical to the first carrierunit 61 in structure except that the second carrier unit 63 carries awafer between the wafer rack 47 and the carrying surface of the stagedevice 50, so that detailed description thereon is omitted.

In the loader 60, the first and second carrier units 61 and 63 eachcarry a wafer from a cassette held in the cassette holder 10 to thestage device 50 disposed in the working chamber 31 and vice versa, whileremaining substantially in a horizontal position. The arms of thecarrier units are moved in the vertical direction only when a wafer isremoved from and inserted into a cassette, when a wafer is carried onand removed from the wafer rack, and when a wafer is carried on andremoved from the stage device 50. It is therefore possible to smoothlycarry a larger wafer, for example, a wafer having a diameter of 30 cm.

Next, how a wafer is carried will be described in sequence from thecassette 14 held by the cassette holder 10 to the stage device 50disposed in the working chamber 31.

As described above, when the cassette is manually set, the cassetteholder 10 having a structure adapted to the manual setting is used, andwhen the cassette is automatically set, the cassette holder 10 having astructure adapted to the automatic setting is used. In this embodiment,as the cassette 14 is set on the up/down table 11 of the cassette holder10, the up/down table 11 is moved down by the elevating mechanism 12 toalign the cassette c with the access port 225.

As the cassette is aligned with the access port 225, a cover (not shown)provided for the cassette is opened, and a cylindrical cover is appliedbetween the cassette 14 and the access port 225 of the mini-environmentto block the cassette and the mini-environment space 21 from theoutside. Since these structures are known, detailed description on theirstructures and operations is omitted. When the mini-environment chamber20 is provided with a gate for opening and closing the access port 225,the gate is operated to open the access port 225.

On the other hand, the arm 612 of the first carrier unit 61 remainsoriented in either the direction M1 or M2 (in the direction M1 in thisdescription). As the access port 225 is opened, the arm 612 extends toreceive one of wafers accommodated in the cassette at the leading end.While the arm and a wafer to be removed from the cassette are adjustedin the vertical position by moving up or down the actuator 611 of thefirst carrier unit 61 and the arm 612 in this embodiment, the adjustmentmay be performed by moving up and down the up/down table 11 of thecassette holder 10, or performed by both.

As the arm 612 has received the wafer, the arm 621 is retracted, and thegate is operated to close the access port (when the gate is provided).Next, the arm 612 is pivoted about the axis O₁—O₁ such that it canextend in the direction M3. Then, the arm 612 is extended and transfersthe wafer carried at the leading end or grabbed by the chuck onto theprealigner 25 which aligns the orientation of the rotating direction ofthe wafer (the rotational direction about the central axis vertical tothe wafer plane) within a predetermined range. Upon completion of thealignment, the carrier unit 61 retracts the arm 612 after a wafer hasbeen received from the prealigner 25 to the leading end of the arm 612,and takes a posture in which the arm 612 can be extended in a directionM4. Then, the door 272 of the gate valve 27 is operated to open theaccess ports 223, 236, and the arm 612 is extended to place the wafer onthe upper stage or the lower stage of the wafer rack 47 within the firstloading chamber 41. It should be noted that before the gate valve 27opens the access ports to transfer the wafer to the wafer rack 47, theaperture 435 formed through the partition wall 434 is closed by the door461 of the gate valve 46 in an air-tight state.

In the process of carrying a wafer by the first carrier unit, clean airflows (as a downflow) in laminar flow from the gas supply unit 231disposed on the housing of the mini-environment chamber to preventparticle from attaching on the upper surface of the wafer during thecarriage. A portion of the air near the carrier unit (in thisembodiment, about 20% of the air supplied from the supply unit 231,mainly contaminated air) is drawn from the suction duct 241 of thedischarging device 24 and emitted outside the housing. The remaining airis recovered through the recovery duct 232 disposed on the bottom of thehousing and returned again to the gas supply unit 231.

As the wafer is placed into the wafer rack 47 within the first loadingchamber 41 of the loader housing 40 by the first carrier unit 61, thegate valve 27 is closed to seal the loading chamber 41. Then, the firstloading chamber 41 is filled with an inert gas to expel air.Subsequently, the inert gas is also evacuated so that a vacuumatmosphere dominates within the loading chamber 41. The vacuumatmosphere within the loading chamber 41 may be at a low vacuum degree.When a certain degree of vacuum is provided within the loading chamber41, the gate valve 46 is operated to open the access port 434 which hasbeen sealed by the door 461, and the arm 632 of the second carrier unit63 is extended to receive one wafer from the wafer receiver 47 with theholding device at the leading end (the wafer is carried on the leadingend or held by the chuck attached to the leading end). Upon completionof the receipt of the wafer, the arm 632 is retracted, followed by thegate 46 again operated to close the access port 435 by the door 461. Itshould be noted that the arm 632 has previously taken a posture in whichit can extend in the direction N1 of the wafer rack 47 before the gate46 is operated to open the access port 435. Also, as described above,the access ports 437, 325 have been closed by the door 452 of the gatevalve 45 before the gate valve 46 is operated to block the interactionbetween the second loading chamber 42 and the working chamber 31 in anair-tight condition, so that the second loading chamber 42 is evacuated.

As the gate valve 46 is operated to close the access port 435, thesecond loading chamber 42 is again evacuated at a higher degree ofvacuum than the first loading chamber 41. Meanwhile, the arm of thesecond carrier unit 61 is rotated to a position at which it can extendtoward the stage device 50 within the working chamber 31. On the otherhand, in the stage device 50 within the working chamber 31, the Y-table52 is moved upward, as viewed in FIG. 2, to a position at which thecenter line X₀—X₀ of the X-table 54 substantially matches an X-axisX₁—X₁ which passes a pivotal axis O₂—O₂ of the second carrier unit 63.The X-table 54 in turn is moved to the position closest to the leftmostposition in FIG. 2, and remains awaiting at this position. When thesecond loading chamber 42 is evacuated to substantially the same degreeof vacuum as the working chamber 31, the door 452 of the gate valve 45is moved to open the access ports 437, 325, allowing the arm 632 toextend so that the leading end of the arm 632, which holds a wafer,approaches the stage device 50 within the working chamber 31. Then, thewafer is placed on the carrying surface 571 of the stage device 50. Asthe wafer has been placed on the carrying surface 571, the arm isretracted, followed by the gate valve 45 operated to close the accessports 437, 325.

The foregoing description has been made on the operation until a waferin the cassette 14 is carried and placed on the stage device. Forreturning a wafer, which has been carried on the stage device andprocessed, from the stage device to the cassette 14, the operationreverse to the foregoing is performed. Since a plurality of wafers arestored in the wafer rack 47, the first carrier unit 61 can carry a waferbetween the cassette and the wafer rack 47 while the second carrier unit63 is carrying a wafer between the wafer rack 47 and the stage device50, so that the testing operation can be efficiently carried out.

In specific, when there are a wafer W, which has been already processed,and a wafer W, which has not yet been processed, in a wafer rack 47 inthe first loading chamber, at first, the wafer which has not yet beenprocessed is transferred to the stage 50 and the processing is started.During this processing, the wafer which has already been processed istransferred from the stage 50 to the wafer rack 47. On the other hand,the other which has not yet been processed is picked up from the waferrack 47 again by the arm, which after having been positioned by apre-aligner, is further transferred to the wafer rack 47 of a loadingchamber 41. This procedure may allow, in the wafer rack 47, the wafer Awhich has already been processed to be substituted by the wafer whichhas not yet been processed, during the wafer being processed.

Alternatively, depending on the way how to use such an apparatus forexecuting an inspection and/or an evaluation, a plurality of stage units50 may be arranged in parallel, so that the wafers may be transferredfrom one wafer rack 47 to each of the stage units 50 thereby applying asimilar processing to a plurality of wafers.

Modifications of Main Housing

FIG. 7 illustrate exemplary modifications to the method of supportingthe main housing 30. In an exemplary modification illustrated in FIG.7(B), a housing supporting device 33 c is made of a thick rectangularsteel plate 331 c, and a housing body 32 c is placed on the steel plate.Therefore, the bottom wall 321 c of the housing body 32 c is thinnerthan the bottom wall 222 of the housing body 32 in the foregoingembodiment. In an exemplary modification illustrated in FIG. 7(B), ahousing body 32 c and a loader housing 40 c are suspended by a framestructure 336 c of a housing supporting device 33 c. Lower ends of aplurality of vertical frames 337 c fixed to the frame structure 336 care fixed to four corners of a bottom wall 321 c of the housing body 32c, such that the peripheral wall and the top wall are supported by thebottom wall. A vibration isolator 37 c is disposed between the framestructure 336 c and a base frame 36 c. Likewise, the loader housing 40is suspended by a suspending member 49 c fixed to the frame structure336. In the exemplary modification of the housing body 32 c illustratedin FIG. 7(B), the housing body 32 c is supported in suspension, thegeneral center of gravity of the main housing and a variety of devicesdisposed therein can be brought downward. The methods of supporting themain housing and the loader housing, including the exemplarymodifications described above, are configured to prevent vibrations frombeing transmitted from the floor to the main housing and the loaderhousing.

In another exemplary modification, not shown, the housing body of themain housing is only supported by the housing supporting device frombelow, while the loader housing may be placed on the floor in the sameway as the adjacent mini-environment chamber. Alternatively, in afurther exemplary modification, not shown, the housing body of the mainhousing is only supported by the frame structure in suspension, whilethe loader housing may be placed on the floor in the same way as theadjacent mini-environment chamber.

Electron Beam Apparatus

An electron optical apparatus 70 (hereafter simply refer to an electronbeam apparatus) of this embodiment will be explained hereafter. Theelectron beam apparatus 70 comprises a optical column 701 fixedlymounted to a housing 32, said optical column containing an electron gun71 a as a device for emitting a charge particle beam, a primary electronoptical system 72 (hereafter simply referred to as a primary opticalsystem) for irradiating a electron beam (hereafter, a electron beam isused for one example of a charge particle beam) emitted from theelectron gun 71 to a sample or substrate and a secondary electronoptical system 74 (hereafter simply referred to as a secondary opticalsystem) to which a secondary electron emitted from the substrate isintroduced, a detecting system 76, and a process control system, asschematically illustrated in FIGS. 8 and 9.

A thermal electron beam source is employed as an electron beam source.An electron emitting member (emitter) is made of LaB₆. Other materialmay be used for the electron emitting member so far as it has a highmelting point (low vapor pressure at high temperature) and a small workfunction. In order to generate a plurality of electron beams, two kindsof method may be used. One is such a method in which firstly a singleelectron beam is emitted from a single emitter (having a singleprojection) and then is passed through a thin plate with a plurality ofapertures formed therein (aperture plate) to generate a plurality ofelectron beams, while in the other method, a plurality of projections isformed on the emitter so that a single electron beam may be emitted froma single projection and thereby a plurality of electron beams may beemitted as a whole. In either method, the electron beam is generated bytaking advantage of such a nature that the projection facilitates a highintensity discharge occurs at a tip thereof. The electron beam generatedin the other types of electron beam source such as a thermal fieldemission type electron beam source may be used.

It is to be noted that the thermal electron beam source is of such amethod in which the electron emitting member is heated to emitelectrons, while the thermal field emission electron beam source is ofsuch a method in which a high electric field is applied to the electronemitting member to emit an electron and further the electron beamemitting section is heated so as to stabilize the electron emission.

The present invention has paid attention to the fact that a shot noisein the secondary electron can be reduced by lowering the shot noise inthe primary electron beam because a main part of the shot noise in thesecondary electron comes from that of the primary electron beam, andaccordingly the electron gun 71 of this embodiment is constructed sothat a desired degree of S/N ratio of the detection signal of thesecondary electron may be accomplished even if a quantity of radiationof the primary electron beam is rather small.

A method for reducing the shot noise in the primary electron beam willbe described below.

Under a condition where the electron gun is controlled by a cathodetemperature, that is, the electron gun is operating in a temperaturelimited region, a shot noise i_(n) emitted from the electron gun may berepresented by the expression below: (See “Communication engineeringhandbook” edited by The Institution of Telecommunications Engineers,1957, p. 471.)i _(n) ²=2e·I _(p) ·B _(f)  (1)where, i_(n) ² is a mean square of a noise current, e is a charge of anelectron, I_(p) is an anode current and B_(f) is a frequency bandwidthof a signal amplifier. When the electron flow is in a space chargelimited region, the expression (1) may be rewritten as:i _(n) ²=Γ²2e·I _(p) ·B _(f)  (2)where, Γ² is a shot noise reduction factor and is smaller than 1.

When the cathode temperature is high enough, Γ² moves to about 0.018 atthe lowest, and the noise current lowers down to 13% of that in the caseof the temperature limited region. Assuming that the secondary electronis nearly equal to the primary electron (secondary electron ≈ primaryelectron), the S/N ratio in this case may be expressed as:S/N=I _(p)/{Γ(2e·I _(p) ·B _(f))^(1/2)}=1/Γ·{I _(p)/(2e·B _(f))^(1/2)}=n ^(1/2)/(Γ·2^(1/2))  (3)When Γ=0.13 is applied to the expression (3), the S/N ratio can beexpressed as:S/N=7.7(n/2)^(1/2)  (4)where, n is a number of the secondary electrons per pixel.

That is, the electron gun operating in the space charge limited regionexhibits a performance equivalent to that in the case where, incomparison with the case of the electron gun operating in thetemperature limited region (TFE case), the 59 (=1/Γ²=1/0.13²) times asmuch as electrons may be required per pixel. Since the latter has higherintensity than that of the former by approximately two digits, thelatter has a possibility to be required larger beam current than theformer by two digits when assuming the same beam diameter and the sameoptical system for both of them, but when a new optical system suitablefor the former is designed, the latter may provide the beam currentlarger than that of the former by one digit. The S/N ratio of the latteris 1/55 of that of the former. In other words, in the electron gun inthe space charge limited region, the measuring time and the dose may beas small as 0.18 times (10/55≈0.18) and 1/55 of those of the electrongun in the temperature limited region, respectively.

Whether or not the electron gun is operating in the space charge limitedregion can be examined by a method described below with reference toFIG. 10.

FIG. 10[A] shows a relation between an electron gun current and acathode heating current. In FIG. 10(A), a region Q₁ is the regionwherein the electron gun current hardly increases in response to anincrease of the cathode heating current, that is, this region Q₁ is thespace charge limited region.

On the other hand, FIG. 10[B] shows a relation between the electron guncurrent and an anode voltage. In FIG. 10(B) a region Q₂ is the regionwherein the electron gun current sharply increases in response to anincrease of the anode voltage, that is, this region Q₂ is also the spacecharge limited region.

As is obvious from the above description, the electron gun may bedetermined to be operating in the space charge limited region if thecathode heating current of the electron gun is increased to measure theelectron gun current and said electron gun current is observed to be inthe saturated condition, the region Q1, or if the anode voltage of theelectron gun is increased to measure the electron gun current and saidelectron gun current is observed to be in the steeply changing region.Accordingly, the condition for operating the electron gun in the spacecharge limited region may be determined.

In the electron gun 71, the heating current or the anode voltage(voltage applied to an anode 712) is set such that the electron gun 71may operate in the space charge limited region, as described above. Acathode 711 of the electron beam 71 is made of monocrystal LaB₆ and hasnine projections each provided with a tip of trapezoidal cone shape,though not shown. These projections are arranged along a circle so thateach of them corresponds to each of a plurality of apertures in a firstmulti aperture plate, which will be described later with reference toFIG. 9. Each tip of these projections has a curvature of radius of about30 μm. Since each electron beam is emitted only from a vicinity of thetip of trapezoidal cone projection, in the case of relatively highelectron gun current such as about 1 mA, for the voltage of 1 kV, theintensity of 1×10⁴ A/cm² sr (1 kV) may be obtained.

The primary optical system 72 serves to irradiate the primary electronbeam emitted from the electron beam 71 onto a surface of a substrate orwafer W to be inspected, and comprises: an electrostatic lens or acondenser lens 721 for focusing the primary electron beam; a first multiaperture plate 723 disposed below said condenser lens 721 and providedwith a plurality of apertures formed therein for forming the primaryelectron beam into a plurality of electron beams or multi-beams; anotherelectrostatic lens or a reduction lens 725 for reducing the primaryelectron beams; an ExB separator 726 including an electromagneticdeflector 727 and an electrostatic deflector 728; and an objective lens729, each being arranged in this order placing the condenser lens 721 ata top position as shown in FIG. 8 such that an optical axis OA₁ of theprimary electron beam emitted from the electron gun is perpendicular tothe surface of the object or wafer W to be inspected.

In order to eliminate an effect of field curvature aberration possiblycaused by the reduction lens 725 and the objective lens 729, a pluralityof apertures 7231 (nine apertures in this embodiment) formed in themulti aperture plate 723 is arranged along a circle around a center ofthe optical axis OA₁, such that projected points of the apertures ontoX-axis may be equally spaced by Lx, as shown in FIG. 9. Each of theapertures may be, for example, a circle with a diameter of about 1 to 10microns, and also it may be of square shape. Further, a position of thefirst multi aperture plate 723 is necessary to be adjusted such that theaperture may be positioned in a point where the primary electron beamemitted from the electron beam 71 has the greatest intensity. For thispurpose, the multi aperture plate 723 is mounted on at least one stageof an XY stage allowing a movement in a plane including the multiaperture plate 723, a Z stage allowing a movement in a directionperpendicular to the plane including the multi aperture plate 723 and aθ stage allowing a rotation of the plane including the multi apertureplate 723, and at least one stage of the XY stage, the Z stage and the θstage each holding the multi aperture plate is adjusted such that theintensity of the plurality of electron beams formed by the multiaperture plate 723 should be uniform and greatest.

The primary optical system 72 further comprises: an electrostaticdeflector 731 for blanking; an electrostatic deflector 733 fordeflecting the primary electron beam so as to cause a scanning motion; aknife edge 732 for blanking; and an axially symmetric electrode 737disposed between the objective lens 729 and the wafer W. The axiallysymmetric electrode 737 is held to be, for example, a potential of −10Vwith respect to a potential 0V of the wafer.

Then the ExB separator 726 will be described with reference to FIG. 11.FIG. 11[A] shows an E×B separator according to a first embodiment of thepresent invention. This separator consists of the electrostaticdeflector 728 and the electromagnetic deflector 727, and is shown inFIG. 11 by a cross sectional views projected onto an X-Y planeperpendicular to the optical axis OA₁ (perpendicular to the paper of thedrawing).

The electrostatic deflector 728 comprises a pair of electrodes(electrostatic deflecting electrodes) 7281 disposed in a vacuumcontainer and generates an electric field in the X-direction. Each ofthese electrostatic deflecting electrodes 7281 is mounted to a vacuumwall 7283 of the vacuum container via an insulating spacer 7282, and adistance Dp between these electrodes is designed to be shorter than alength 2 Lp along the Y-direction of the electrostatic deflectingelectrodes 7281. Owing to this design, an area where an electric fieldintensity generated around a Z axis or the optical axis OA₁ is uniformmay be made relatively wider, wherein ideally if Dp<Lp, the area withuniform electric field intensity could be made further wider.

That is, since in an area within a distance of Dp/2 from an end of theelectrode, the electric field intensity is not uniform, the area withalmost uniform electric field intensity is in a central area or 2Lp-Dparea which excludes the end areas with non-uniform electric fieldintensity. This means that a condition of existence of the uniformelectric field intensity is 2Lp>Dp, and in addition, designing to beLp>Dp makes the uniform electric field area further wider.

On an outside of the vacuum wall 7283 is provided an magnetic deflectorfor generating a magnetic field in the Y-direction. The magneticdeflector 727 comprises an magnetic coil 7271 and another magnetic coil7272, wherein each of these coils generates a magnetic field in the X-and the Y-directions respectively. It is to be noted that although themagnetic field in the Y-direction can be generated only by the coil7272, the coil 7271 for generating the magnetic field in the X-directionis also mounted in order to improve an orthogonality between theelectric field and the magnetic field. That is, the orthogonalitybetween the electric field and the magnetic field can be improved byoffsetting a magnetic field component in the +X direction generated bythe coil 7272 with a magnetic field component in the −X directiongenerated by the coil 7271.

Each of these coils 7271 and 7272 for generating magnetic field isconstituted of two pieces in order to be arranged on the outside of thevacuum container, so that these two pieces may be attached onto thevacuum wall 7283 from both sides respectively and may be clamped tightlyby screw or the like at a portion 7 so as to be made into one unit.

An outermost layer 7273 of the E×B separator is constructed as a yokemade of permalloy or ferrite. Similar to the coils 7271 and 7272, theoutermost layer 7273 may be made as two pieces and attached onto anoutside of the coil 7272 to be formed into one unit by screwing at aportion 7274.

FIG. 11[B] shows another ExB separator according to a second embodimentof the present invention by a cross sectional view projected on a planeorthogonal to the optical axis. This ExB separator according to thesecond embodiment is different from that of the first embodiment shownin FIG. 11[A] in that six poles of electrostatic deflecting electrodes7281′ are provided therein. In FIG. 11[B], any components correspondingto those of the ExB separator shown in FIG. 11[A] will be designated bythe same reference numerals added by “′” (dash), and the descriptiontherefor will be omitted. To each of these electrostatic deflectingelectrodes 7281′ is applied a voltage proportional to cos θ_(i), whichis represented as k·cos θ_(i) (k is constant), where θ_(i) (i=0, 1, 2,3, 4, 5) is an angle formed between a line connecting a center of eachelectrode to the optical axis and a direction of the electric field(X-axis direction). It is to be noted that the θ_(i) is an arbitraryangle.

Since also the second embodiment shown in FIG. 11[B] can generate onlythe electric field in the X-axis direction similar to the firstembodiment, coils 7271′ and 7272′ for generating the magnetic fields ofX-axis direction and of Y-axis direction, respectively, are provided tocorrect the orthogonality.

The embodiment shown in FIG. 11[B] can make the area with uniformelectric field intensity further wider than the embodiment shown in FIG.11[A].

Although the coil for generating magnetic field has been formed into asaddle type in the embodiments shown in FIGS. 11[A] and 11[B], a coil oftoroidal type may be employed.

The secondary optical system 74 comprises two magnifying lenses 741 and743, which make up a two stage electrostatic lens, for passingtherethrough a secondary electron separated from the primary opticalsystem by the ExB separator 727, and a second multi aperture plate 745.Each of apertures 7451 formed in the second multi aperture plate 745 isadapted, as shown by a broken line in FIG. 9, to correspond one-to-oneto each of the apertures 7231 formed in the first multi aperture plate723 of the primary optical system, wherein the aperture 7451 of thesecond multi aperture plate 745 is a circular hole with a diameterlarger than that of the aperture 7231 of the first multi aperture plate723.

The detection system 76 comprises a plurality of detectors 761 (ninedetectors in this embodiment) each disposed corresponding to andadjacent to each aperture 7451 of the second multi aperture plate 745 ofthe secondary optical system 74, and each of the detectors 761 iselectrically connected to an image data processing section 771 of theprocess control system 77 via an A/D converter (including amplifier)763. It is to be noted that though only one detector 761 has beenconnected to the image processing section 771 in FIG. 8, respectivedetectors are connected to the image data processing section viarespective independent A/D converters 763. Further, the image processingsection 771 is also connected to the electrostatic deflector 733 so thata scanning signal for deflecting the primary electron beam may besupplied to the electrostatic deflector 733. As an element for thedetectors may be used, for example, a PN junction diode which directlydetects an electron beam intensity or a PMT (photomultiplier) whichdetect a light emitting intensity through a scintillator which becomesluminous by electron.

The image processing section 771 may convert an electric signal suppliedfrom respective A/D converter 763 to a binary information by setting anappropriate threshold voltage, and then may convert the binary signalinto an image data. For this purpose, the scanning signal for deflectingthe primary electron beam, which is supplied from the electrostaticdeflector 733 to the image processing section 771, may be used. Theimage processing section 771 may compare the obtained image data with areference circuit pattern, while storing thus obtained image data in anappropriate memory. Thereby, a plurality of circuit patterns, or thesame number of circuit patterns with that of the primary electron beams,on the wafer W may be subjected to the inspection simultaneously.

It is to be noted that in the embodiment shown in FIG. 8, the image dataprocessing section 771 can use various kinds of reference circuitpatterns in order to compare therewith an image data representing acertain circuit pattern on the wafer W, that is, for example, an imagedata obtained in the same place on the other chip different from thatscanned for generating said image data to be compared may be used.

An operation of the electron beam apparatus with an above configurationwill now be described. The primary electron beam emitted from theelectron gun 71 is converged by the condenser lens 721 in the primaryoptical system 72 to form a crossover at a point P1 of knife edge 732.On the other hand, the primary electron beam converged by the condenserlens 721 passes through the plurality of apertures 7231 of themulti-aperture plate 723 to form into a plurality of primary electronbeams (nine beams in this embodiment), which are forcused by thereducing lens 725 so as to be projected onto a point P2. After beingfocused onto the point P2, the beams are further focused onto a surfaceof a wafer W by the objective lens 729. On the other hand, the deflecter733 disposed between the reducing lens 725 and the objective lens 726deflects the primary electron beams so as to scan the surface of thewafer W.

The plurality of focused primary electron beams are irradiated onto thewafer W at a plurality of points thereon, and secondary electrons areemitted from said plurality of points. Those secondary electrons areattracted by an electric field of the objective lens 729 to be convergednarrower, and then deflected by the E×B separator 726 so as to beintroduced into the secondary optical system 74. The secondary electronimage is focused on a point P3 which is much closer to the deflector 726than the point P2. This is because the primary electron beam has theenergy of 500 eV on the surface of the wafer, while the secondaryelectron beam only has the energy of a few eV.

Each of the images of the secondary electrons focused at the point P3 isfocused by the two-stage magnifying lenses 741 and 743 onto each of thecorresponding apertures 7451 of the multi-aperture detection plate 745to be formed into an image, so that each of the detectors 761 disposedcorrespondingly to each of the apertures 7451 detects the image. Each ofthe detectors 761 thus detects the electron beam and converts it into anelectric signal representative of its intensity. The generated electricsignals are output from respective detectors 761, and after beingconverted respectively into digital signals by the A/D converter 763,they are input to the image processing section 771 of the processcontrol system 77. The image processing section 763 converts the inputdigital signals into image data. Since the image processing section 763is further supplied with a scanning signal for deflecting the primaryelectron beam, the image processing section 763 can display an imagerepresenting the surface of the wafer. Comparing this image with areference pattern that has been pre-set in a setting device (not shown)allows to determine whether or not the pattern on the wafer W beinginspected (evaluated) is acceptable.

Further, the line width of the pattern formed on the surface of thewafer W can be measured in such a way that the pattern to be measured onthe wafer W is moved by a registration to the proximity of the opticalaxis of the primary optical system, and the pattern is then line-scannedto extract the line width evaluation signal, which in turn isappropriately calibrated.

Irradiation of the primary electron beams onto a wafer while scanningthem with respect to the wafer may be practiced as shown in FIG. 12. Forsimplicity of explanation, a case wherein the number of electron beamsare four (EB1 to EB4) will be explained. Each irradiation point Ebp1 toEbp4 of each primary electron beam designates the irradiating point ofthe primary electron beams which scans from the left side to the rightside in the X direction in corresponding, respective scanning areas SA1to SA2. The size of one electron beam is determined such that eachprimary electron beam can scan the area having a width of 50 μm. Whenthe irradiation point of the electron beam reaches the right side in thecorresponding scanning area, the irradiating point is moved back to theleft side of the scanning area. On the other hand the stage devicecontinuously moves the wafer with predetermined speed in the Ydirection.

In this regard, it is required to make special arrangements in order tominimize the affection by the three aberrations, i.e., the distortioncaused by the primary optical system, the axial chromatic aberration,and the filed astigmatism, when the primary electron beams passedthrough the apertures of the multi-aperture plate 723 in the primaryoptical system are focused onto the surface of the wafer W and then thesecondary electrons emitted from the wafer W are formed into an image onthe detector 761.

It is to be noticed that, with respect to the relationship between thespacing of a plurality of primary electron beams and the secondaryoptical system, any space between the primary electron beams made longerthan the aberration by the secondary optical system may eliminate thecross talks among the plurality of beams.

Although there has been described above an example in which a pluralityof tips of the cathode of the electron gun is arranged along a circle,the plurality of tips may be arranged on a line. In that case, theapertures formed on the first multi aperture plate 723 as well as thoseon the second multi aperture plate 745 must be arranged along respectivelines at positions corresponding to the tips of the cathode.

According to an actual machine test having been conducted by using theelectron beam apparatus shown in FIG. 8, a beam current of 3nA wasobtained as a beam current for each of nine electron beams when a beamdiameter of 10 nm was employed. In comparison with the beam current of150 nA during an operation within the temperature limited region, theS/N ratio was in a comparative degree. Since a total beam current of thenine electron beams was 27 nA, which was small enough in comparison withthe 150 nA, a beam blur possibly caused by the space charge effect hadalmost no effect. Further, because of nine electron beams being used,nine times as fast as inspection speed may be expected in comparisonwith a case of one electron beam.

Then, with reference to FIG. 13, a detailed configuration of the imagedata processing section 771 of the electron beam apparatus shown in FIG.8 will be described. The image data processing section 771 comprises asub-image data storage sub system 7711, an image data re-arranging subsystem 7712, an inter-sub-image overlap processing sub system 7713, aninspection image data storage sub system 7714, a reference image datastorage sub system 7715, and a comparison sub system 7716. The sub-imagedata storage sub system 7711 serves to receive and to store a sub-imagedata detected by each detector 761 for detecting the secondary electron,and has a storage area corresponding to each detector. The image datare-arranging sub system 7712 serves to re-arrange the sub-image datastored in the sub-image data storage sub system 7711 so as to match theX-Y coordinates of respective multi beams, while the inter-sub-imageoverlap processing sub system 7713 serves to determine a boundarybetween the sub-images and/or to decide either of the sub-image datashould be employed. Re-arranged image data is stored in the inspectionimage data storage sub system 7714. The comparison sub system 7716compares the image data stored in the inspection image data storage subsystem 7714 with the reference image data stored in the reference imagedata storage sub system 7715, and outputs a result of the comparison.

FIG. 14 illustrates an operation of the image data re-arranging subsystem 7712 shown in FIG. 13. As having been described with reference toFIG. 8, the first and the second multi aperture plates 723 and 745 aredesigned such that arrangement positions of the apertures in the firstand the second multi aperture plates 723 and 745 (and the detectors 761)may relatively correspond to each other, and projected points on theX-axis of the beam spots irradiated through the apertures in the firstmulti aperture plate 723 onto the wafer W may be spaced withapproximately equal distances. Therefore, the beam spots generated whenthe multi beams having passed through the plurality of apertures in thefirst multi aperture plate 723 are irradiated onto the wafer W are alsospaced with approximately equal distances when they are projected ontothe X-axis. That is, in FIG. 14, when the X-Y coordinates of the multibeams (i.e. beam spots) EB1 to EB9 formed along a circle around a centerof the optical axis are designated by (x₁, y₁)˜(x₉, y₉), a relationthereof may be expressed as:x ₁ −x ₂ ≈x ₂ −x ₉ ≈x ₉ −x ₃ ≈x ₃ −x ₈ ≈x ₈ −x ₄ ≈x ₄ −x ₇ ≈x ₇ −x ₅ ≈x₅ −x ₆ ≈Lx (constant, as shown in FIG.9).

When a sample or the wafer W is evaluated by using the electron beamapparatus shown in FIG. 8, the multi beams EB1 to EB 9 aresimultaneously irradiated onto the wafer W while continuously moving thestage unit 50 on which the wafer W is mounted in the Y-axis directionand at the same time controlling the multi beams so as to scan in theX-direction by a line width d+Δ. That is, adjacent two beams arecontrolled so as for their scanning areas to overlap with each other inthe X-direction by Δ. Thus, when the areas scanned by the multi beamsEB1 to EB9 are designated by SA1 to SA9, the multi beams EB1 to EB9raster-scan the corresponding areas SA1 to SA9 respectively.

The secondary electron beams emitted from a surface of the wafer W by anirradiation of the multi beams are passed through the apertures of thesecond multi aperture plate 745 to be detected by the correspondingdetectors 761 for detecting the secondary electrons, and what aredetected by the detectors 761 are stored in the respective storage areasin the sub-image data storage sub system 7711 as the sub-image data. Theimage re-arranging sub system 7712 re-arranges the sub-image data storedin the storage sub system 7711 so as to be arranged in a order of thedetectors from 761-1 to 761-9 (wherein, the detectors 761-1 to 761-9correspond to the multi beams EB1 to EB9 respectively), that is, in thearea order of SA1, SA2, SA9, SA3, SA8, SA4, SA7, SA5, and then SA6.

At that time, the displacement of the detectors 761-1 to 761-9 in theY-axis direction should be taken into account. For example, as to thedetectors 761-1 and 761-2, time T necessary for the movement of thestage unit 50 by a distance y₂−y₁ is measured in advance and arrangesthe image data rearranging sub system 7712, adjacent to a sub-image datafrom the detector 761-1 obtained by a certain scanning in the X-axisdirection, another sub-image data obtained from the detector 761-2 atthe time T after said certain scanning. Thereby, not only an arrangementrelation of the X coordinate but also the Y coordinate value of theimage data adjacently arranged in the X-direction can be made coincidentwith each other. Alternative method may be employed in which thedistance y₂−y₁ is converted into a number of the pixels so as todisplace their position by that number of pixels.

The overlap Δ between adjacent two areas is determined by theinter-sub-image overlap processing sub system 7653, for example, in sucha manner as described below. An area (B) in FIG. 14 designates theoverlap between the areas SA1 and SA2, and Pt in the area (B) in FIG. 14designates a pattern to be evaluated, wherein a boundary line Bol isdetermined within the overlap Δ so as not to cross the pattern such thata sub-image data from the detector 761-1 corresponding to the beam EB1is employed for a right side area of the boundary Bol and anthersub-image data from the detector 761-2 corresponding to the beam EB2 isemployed for a left side area of the boundary Bol, and then thesesub-image data are combined. That is, the boundary is determined in sucha manner that the crossing of the boundary between the sub-images withthe patterns may be minimized. Other overlaps may be processed in thesame manner.

Among these image data combined in the manner described above, only theimage data within an area to be inspected EA of the wafer W are storedin the inspection image data storage sub system 7714.

When all the image data within an area to be inspected EA on the wafer Wcannot be obtained by a single scanning, that is, as shown in FIG. 14,when there still exists an area to be scanned in the right side of thearea SA6, the stage unit 50 may be shifted in the X-axis direction sothat the new area adjacent to the area SA6 can be scanned by the beamEB1 to obtain the image data in the same manner as described above.

When any defects is to be detected, the comparison sub system 7716compares the image data stored in the inspection image data storage subsystem 7714 with the reference image data stored in the reference imagedata storage sub system 7715, so that the defect on the wafer W may bedetected. Alternatively, a plurality of combined images for a pluralityof wafer expected to have the same pattern may be obtained to comparethe image data with each other, thereby determining there being thedefect at a portion of a certain wafer when said portion exhibits animage data different from other most image data.

When a line width is to be detected, an appropriate method may beemployed to measure the line width.

Although there has been described the case where the X coordinates ofthe beam spots of the primary electron beams are spaced withapproximately equal distances, they may not be necessarily spaced withequal distance. Alternatively, for example, distances between beams inthe X-axis direction may be measured to be converted into a number ofpixels, thereby shifting the images by this number of pixels. In thiscase, the distance on the X coordinate between the irradiation spots maybe varied.

Pre-Charge Unit

As shown in FIG. 1, a pre-charge unit 81 is disposed in a workingchamber 31, adjacent to a optical column 701 of an electronic opticalapparatus 70. Since this inspection apparatus is of a type in which anelectron beam is irradiated a substrate or wafer to be inspected byscanning it, and thereby a device pattern or the like formed on asurface of the wafer is inspected, information such as secondaryelectrons emitted by the irradiation of the electron beam is utilized asan information of the wafer surface. Sometimes, depending on a conditionincluding a material of the wafer, an energy level of the irradiatedelectron or the like, the wafer surface may be charged-up. Further,depending on the locations on the wafer, some locations might be morestrongly charged-up than other locations. If there are non-uniformdistribution in a charging amount on the wafer, the information of thesecondary electron beam is made to be non-uniform, which makes it hardto obtain an accurate information.

Accordingly, in the present embodiment, there is provided a pre-chargeunit 81 having a charged particle irradiating section 811 in order toprevent this non-uniform distribution. In order to prevent a non-uniformdistribution in charging, before the electrons for inspection beingirradiated onto a predetermined location of the wafer to be inspected,the charged particles are irradiated from the charged particleirradiating section 811 of the pre-charge unit thereto, thus preventingthe non-uniform charging from occurring. The charging on the wafersurface is detected by forming and evaluating an image of the wafersurface in advance, and based on a result of the detection, thepre-charge unit 81 is operated. Further, in this pre-charge unit, theprimary electron beam may be irradiated with some gradation.

In this pre-charge unit, the primary electron beam may be irradiatedwith an out of focus condition.

In some method for inspecting a sample for any electric defects, such afact may be used that when a portion to be insulated is not in theinsulated condition by some reason, a voltage in that portion isdifferent from that in the insulated condition.

This is conducted in such a manner that firstly a voltage difference isgenerated between a voltage in a portion to be insulated essentially andthat of another portion which should have been insulated but is not inthe insulated condition due to some reason, by applying a charge to thesample in advance; secondly the data with voltage difference is obtainedby irradiating the beam according to the present invention; and finallya non-insulated condition is detected by analyzing the obtained data.

Potential Applying Mechanism

Referring next to FIG. 15, the potential applying mechanism 83 applies apotential of plus or minus several volts to a carrier of a stage, onwhich the wafer is placed, to control the generation of secondaryelectrons based on the fact that the information on the secondaryelectrons emitted from the wafer (secondary electron yield) depend onthe potential on the wafer. The potential applying mechanism 83 alsoserves to decelerate the energy originally possessed by irradiatedelectrons to provide the wafer with irradiated electron energy ofapproximately 100 to 500 eV.

As illustrated in FIG. 15, the potential applying mechanism 83 comprisesa voltage applying device 831 electrically connected to the carryingsurface 571 of the stage device 50; and a charging detection/voltagedetermining system (hereinafter detection/determining system) 832. Thedetection/determining system 832 comprises a monitor 833 electricallyconnected to an image forming unit 771 of the detecting system 76 in theelectron beam apparatus 70; an operator 834 connected to the monitor833; and a CPU 835 connected to the operator 834. The CPU 835 supplies asignal to the voltage applying device 831.

The potential applying mechanism 83 is designed to find a potential atwhich the wafer under testing is hardly charged, and to apply suchpotential to the carrying surface 541.

Electron Beam Calibration Mechanism

Referring next to FIG. 16, the electron beam calibration mechanism 85comprises a plurality of Faraday cups 851, 852 for measuring a beamcurrent, disposed at a plurality of positions in a lateral region of thewafer carrying surface 541 on the turntable. The Faraday cups 851 areused for a fine beam (approximately Φ 2 μm), while the Faraday cups 852are used for thick beams (approximately Φ 30 μm). The Faraday cups 851for a fine beam measures a beam profile by driving the turntable step bystep, while the Faraday cups 852 for a wide beam measure a total amountof currents. The Faraday cups 851, 852 are mounted on the wafer carryingsurface 541 such that their top surfaces are coplanar with the uppersurface of the wafer W carried on the carrying surface 541. In this way,the primary electron beam emitted from the electron gun is monitored atall times. This is because the electron gun cannot emit a constantelectron beam at all times but varies in the emitting amount as it isused over time.

Alignment Controller

The alignment controller 87, which aligns the wafer W with the electronoptical apparatus 70 using the stage system 50, performs the control forrough alignment through wide field observation using the opticalmicroscope 871 (a measurement with a lower magnification than ameasurement made by the electron optical system); high magnificationalignment using the electron optical system of the electron opticalapparatus 70; focus adjustment; testing region setting; patternalignment; and so on. The wafer is tested at a low magnification usingthe optical system in this way because an alignment mark must be readilydetected by an electron beam when the wafer is aligned by observingpatterns on the wafer in a narrow field using the electron beam forautomatically testing the wafer for patterns thereon.

The optical microscope 871 is disposed on the housing 30 (alternatively,may be movably disposed within the housing 30), with a light source, notshown, being additionally disposed within the housing 30 for operatingthe optical microscope. The electron optical system for observing thewafer at a high magnification shares the electron optical systems(primary optical system 72 and secondary optical system 74) of theelectron optical apparatus 70. The configuration may be generallyillustrated in FIG. 17. For observing a point to be observed on a waferat a low magnification, the X-stage 54 of the stage device 50 is movedin the X-direction to move the point to be observed on the wafer into aview field of the optical microscope 871. The wafer is viewed in a widefield by the optical microscope 871, and the point to be observed on thewafer is displayed on a monitor 873 through a CCD 872 to roughlydetermine a position to be observed. In this event, the magnification ofthe optical microscope may be changed from a low magnification to a highmagnification.

Next, the stage device 50 is moved by a distance corresponding to aspacing δx between the optical axis of the electron optical apparatus 70and the optical axis of the optical microscope 871 to move the point tobe observed on the wafer, previously determined by the opticalmicroscope 871, to a point in the field of the electron opticalapparatus 70. The distance δx between the axis O₃—O₃ of the electronoptical apparatus and the axis O₄—O₄ of the optical microscope 871 ispreviously known (while it is assumed that the electron-optical system70 is deviated from the optical microscope 871 in the direction alongthe X-axis in this embodiment, they may be deviated in the Y-axisdirection as well as in the X-axis direction), such that the point to beobserved can be moved to the viewing position by moving the stage device50 by the distance δx. The point to be observed has been moved to theviewing position of the electron optical apparatus 70, the point to beobserved is imaged by the electron optical system at a highmagnification for storing a resulting image or displaying the image onthe monitor 765 through the CCD 761.

After the point to be observed on the wafer imaged by the electronoptical system at a high magnification is displayed on the monitor 765,displacement of the stage device 50 with respect to the center ofrotation of the turntable 54 in the wafer rotating direction, that isdisplacement δθ of the stage device 50 with respect to the optical axisO₃—O₃ of the electron optical system in the wafer rotating direction aredetected in a known method, and displacement of a predetermined patternwith respect to the electron optical apparatus in the X-axis and Y-axisis also detected. Then, the operation of the stage device 50 iscontrolled to align the wafer based on the detected values and data on atesting mark attached on the wafer or data on the shape of the patternson the wafer which have been acquired in separation.

Control System

A control system comprises a main controller, a controlling controller,and a stage controller as main components, though not shown.

The main controller is provided with a man-machine interface throughwhich an operator manipulates the main controller (a variety ofcommands/instructions, an entry of recipe and the like, direction ofinspection start, switching between an automatic and a manual inspectionmodes, an input of all of the commands required in the manual inspectionmode and so forth). In addition, the main controller also performs suchjobs as: a communication with a host computer in a plant; a control ofthe vacuum evacuating system; a transfer of a sample such as a wafer; acontrol of position alignment; a transmission of commands or informationto other controlling controllers or the stage controller; and a receiptof information or the like. Further, the main controller also is incharge of such functions as: an acquisition of an image signal from anoptical microscope; a stage vibration compensating function forcompensating for possible deterioration in image by feeding back afluctuating signal of the stage to the electronic optical system; and anautomatic focal point compensating function for detecting a displacementof a usage observation point in the Z direction (the direction along theoptical axis OA₁ of the first optical system) and feeding it back to theelectron optical system so as to automatically compensating for thefocal point. The transmitting/ receiving operation of the feedbacksignal or the like to/from the electronic optical system as well as thetransmitting/receiving operation of the signal to/from the stage areperformed via the controlling controller or the stage controllerrespectively.

The controlling controller is mainly in charge of a control of theelectron optical system (such as a control of high precision powersource for the electron gun, the lenses, the aligner, the Wien filter orthe like). In specific, the controlling controller performs, forexample, such a control (continuous control) operation as an automaticvoltage setting for respective lens systems and the aligner in responseto respective operation modes, so that a constant electron current maybe regularly irradiated onto the irradiation region even if themagnification is changed, and the voltage to be applied to respectivelens systems, the aligner or the like may be automatically set inresponse to the magnification.

The stage controller is mainly in charge of a control for a movement ofthe stage to allow a precise movement in the X- and the Y-directions onthe order of μm (with tolerance of about +/−0.5 μm). Further, in thepresent stage, a control in the rotational direction (θ control) is alsoperformed with a tolerance equal to or less than about +/−0.3 seconds.

Inspection Procedure

Generally, since an inspection apparatus using an electron beam israther expensive and also the throughput thereof is rather lower thanthat provided by other processing apparatuses, this type of inspectionapparatus is currently applied to a wafer after an important process(for example, etching, film deposition, or CMP (chemical and mechanicalpolishing) planarization process) which is considered that theinspection is required most.

A wafer W to be inspected is, after having been positioned on an ultraprecise stage unit through a loading chamber, secured by anelectrostatic chucking mechanism or the like, and then a detectinspection is conducted according to a procedure (inspection flow) shownin FIG. 18. At first, if necessary, a position of each of dice ischecked and/or a height of each location is sensed, and those values arestored. Adding to that, an optical microscope is used to obtain anoptical microscope image in an area to be observed possibly includingdefects or the like, which may also be used in, for example, thecomparison with an electron beam image. Then, recipe informationcorresponding to the kind of the wafer (for example, after which processthe inspection should be applied; which is the wafer size, 200 mm or 300mm, and so on) is entered into the apparatus, and subsequently, after adesignation of an inspection place, a setting of an electronic opticalsystem and a setting of an inspection condition having being executed, adefect inspection is conducted typically at real time whilesimultaneously obtaining the image. A fast data processing system withan algorithm installed therein executes an inspection, such as thecomparisons between cells, between dice or the like, and any resultswould be output to a CRT or the like and stored in a memory, if desired.Those defects include a particle defect, an irregular shape (a patterndefect) and an electric defect (a broken wire or via, a bad continuityor the like), and the fast data processing system also can automaticallyand at real-time distinguish and categorize them according to a defectsize, or whether their being a killer defect (a critical defect or thelike which disables a chip). The detection of the electric defect may beaccomplished by detecting an irregular contrast. For example, since alocation having a bad continuity would generally be charged intopositive level by an electron beam irradiation (about 500 eV) andthereby its contrast would be decreased, the location of bad continuitycan be distinguished from normal locations. The electron beamirradiation device in that case designates an electron beam source(source for generating thermoelectron, UV/photoelectron) with lowerpotential (energy) arranged in order to emphasize the contrast by apotential difference, in addition to the electron beam irradiationdevice used for a regular inspection. Before the electron beam forinspection being irradiated against the objective region for inspection,the electron beam having that lower potential energy is generated andirradiated.

Cleaning of Electrode

As the electron beam apparatus according to the present invention beingoperated for a long time, an organic substance would be deposited on avariety of electrodes used for forming or changing the electron beam.Since the insulating material gradually depositing on the surface of theelectrodes by the electric charge affects reversely on the forming ordeflecting mechanism for the electron beam, accordingly those depositedinsulating material must be removed periodically. To remove theinsulating material periodically, an electrode adjacent to the regionwhere the insulating material has been deposited is used to generate theplasma of hydrogen, oxygen, fluorine or compound including them (HF, O₂,H₂O, C_(M)F_(N) or the like) in the vacuum and to control the plasmapotential in the space to be a potential level (several kV, for example,20V-5 kV) where the spatter would be generated on the electrode surface,thereby allowing only the organic substance to be oxidized, hydrogenatedor fluorinated and thereby removed.

Next, an embodiment of a method of manufacturing a semiconductor deviceaccording to the present invention will be described with reference toFIGS. 19 and 20.

FIG. 19 is a flow chart illustrating an embodiment of a method ofmanufacturing a semiconductor device according to the present invention.Manufacturing processes of this embodiment include the following mainprocesses:

(1) a wafer manufacturing process for manufacturing a wafer (or a waferpreparing process for preparing a wafer);

(2) a mask manufacturing process for manufacturing masks for use inexposure (or mask preparing process for preparing masks);

(3) a wafer processing process for performing processing required to thewafer;

(4) a chip assembling process for cutting one by one chips formed on thewafer and making them operable; and

(5) a chip testing process for testing complete chips.

The respective main processes are further comprised of severalsub-processes.

Among these main processes, the wafer fabricating process set forth in(3) exerts critical affections to the performance of resultingsemiconductor devices. This process involves sequentially laminatingdesigned circuit patterns on the wafer to form a large number of chipswhich operate as memories, MPUs and so on. The wafer fabricating processincludes the following sub-processes:

(A) a thin film forming sub-process for forming dielectric thin filmsserving as insulating layers, metal thin films for forming wirings orelectrodes, and so on (using CVD, sputtering and so on);

(B) an oxidation sub-process for oxidizing the thin film layers and thewafer substrate;

(C) a lithography sub-process for forming a resist pattern using masks(reticles) for selectively fabricating the thin film layers and thewafer substrate;

(D) an etching sub-process for fabricating the thin film layers and thesubstrate in conformity to the resist pattern (using, for example, dryetching techniques);

(E) an ion/impurity inplantation/diffusion subprocess;

(F) a resist striping sub-process; and

(G) a sub-process for testing the fabricated wafer;

As appreciated, the wafer fabrication process is repeated a number oftimes equal to the number of required layers to manufacturesemiconductor devices which operate as designed.

FIG. 20 is a flow chart illustrating the lithography sub-process whichforms the core of the wafer processing process in FIG. 12. Thelithography sub-process includes the following steps:

(a) a resist coating step for coating a resist on the wafer on whichcircuit patterns have been formed in the previous process;

(b) a resist exposing step;

(c) a developing step for developing the exposed resist to produce aresist pattern; and

(d) an annealing step for stabilizing the developed resist pattern.

Since the aforementioned semiconductor device manufacturing process,wafer fabrication process and lithography process are well known, andtherefore no further description will be required.

When the defect testing method and defect testing apparatus according tothe present invention are used in the testing sub-process set forth in(G), any semiconductor devices even having submicron (sized) patternscan be tested at a high throughput, so that a total inspection can alsobe conducted, thereby making it possible to improve the yield rate ofproducts and prevent defective products from being shipped.

It is to be noted that although in the above embodiment, there has beendescribed an example shown in FIGS. 1 and 2 where only a single electronbeam apparatus 70 is installed, a plurality of electron beam apparatusesmay be arranged side-by-side, as shown in FIG. 21, to inspect aplurality of regions simultaneously.

That is, FIG. 21(A) is a plan view of an example of arrangement wherefour optical columns (each optical column includes one electron beamapparatus respectively) are arranged on a line, while FIG. 21(B) is aplan view of another example of arrangement where six optical columns,each having an optical axis OA₂, are arranged in a matrix of two rows bythree columns. In the examples shown in FIGS. 21(A) and 21(B), a singleoptical columns irradiates a plurality of electron beams (each one isdesignated by a symbol “EB”), which is then detected by a multidetector. The multi detector comprises a plurality of detector elements761, each detecting a single electron beam EB. A maximum outer diameterof an area on a wafer surface irradiated by a plurality of electronbeams of one optical column is designated respectively by symbols Sr1 toSr6. In the examples shown in FIGS. 21(A) and 21(B), each of theplurality of optical columns is arranged so as not to interface witheach other, so that a wide area of wafer surface may be inspected by anumber of optical columns at once, thereby accomplishing high throughputin the wafer inspection process. In the example shown in FIG. 21(A), thewafer surface is continuously moved in a direction perpendicular to therow of the optical columns (designated by an arrow Ar1) in order toinspect entire wafer W.

Variation of the Inspection Apparatus

Then, a specific example of an inspection method of a circuit patternformed on a substrate or the wafer W will be described. FIGS. 22 and 23show typical example in the case of forming a circuit pattern by usingan electron beam lithography. That is, a semiconductor chip SCT isdivided into a plurality of stripes St extending in a Y-axis directionwith a width in a X-direction of, for example, 5 mm, and a mask patternis transferred onto the wafer while continuously moving the stage unit50 with said semiconductor chip mounted thereon along each stripe in theY-direction. Further, one stripe is divided into a plurality of primaryfields of views, each being defined by a Y-direction size of 250 μm andan X-direction size of 5 mm and designated by VFp, which in turn isfurther divided into a plurality of secondary fields of view, each beingdefined by 250 μm square and designated by VFs, wherein the transfer isexecuted for each secondary field of view. That is, one mask is preparedfor each secondary field of view, which is a component of the primaryfield of view, and a circuit portion is transferred by scanning with thebeam each secondary field of view one-by-one.

When the circuit pattern is formed by the above-described method, aportion where the defect is most likely to occur is in a boundarybetween one stripe St and an adjacent stripe St, a portion where thedefect is second-most likely to occur is in a boundary between theprimary fields of view VFps, and a portion where the defect isthird-most likely to occur is in a boundary between the secondary fieldsof view VFss. A portion with the widest fluctuation exhibits in the sameorder of boundary portion between stripes, that between the primaryfields of view, and that between the secondary fields of view.

Accordingly, in this embodiment, an evaluation apparatus is equippedwith an inspection mode for inspecting each boundary between the stripesdesignated by BAst with a width of 200 μm (seven portions in FIG. 22).When more precise evaluation is expected, a mode for inspecting aboundary area between the primary fields of view designated as BApshould be employed, and more preferably a mode for inspecting a boundaryarea between the secondary fields of view designated as BAs should beemployed additionally. Applying a sampling inspection with a certainpriority as described above allows most defects to be detected whilereducing an inspection time to be several to several ten percents incomparison with the case of 100% inspection.

In the electron beam apparatus, the optical system has small aberrationand distortion in a central portion of the field of view, andaccordingly a reliable evaluation may be accomplished when the centralportion of the field of view is used for the measurement. That is, aprobability of missing any defects may be made lower when the boundaryarea could be necessarily evaluated by using the central portion of thefield of view, as showing the stripe width by BAo, even if both of theboundary area and the other areas are to be inspected together.Moreover, a probability of detrmining normal patterns as defects may bemade lower.

The deflectors for scanning 733 and 728 are adapted to scan the surfaceof the wafer W with the irradiation points of the primary electron beamin the X-direction, and a scanning distance is controlled to be “anX-directional distance between irradiation points of the primaryelectron beams plus α”. That is, the a designates a dimension in theX-direction of the area to be double scanned, which is 0.3 to 3 mm.

When the boundary between the stripes on the surface of the wafer W isto be inspected in this electron beam apparatus, the stage unit 50continuously moves the wafer in the Y-direction for the inspection.During this operation, the scanning deflectors 733 and 728 control theirradiation point of each primary electron beam to scan in theX-direction by the X-directional distance between the electron beamsplus α. For example, the boundary between the stripes described above isto be inspected by a width of 200 μm, the X-directional distance betweenthe primary electron beam irradiation points is set to be 23 μm, theneach primary electron beam irradiation point scans a width of 23+α, andas a whole, an inspection width of 23×9+α (=200 μm+α) may beaccomplished.

Upon executing a defect inspection, the image obtained by scanning asdescribed above is compared with an image without defect, which has beenstored previously in a memory, to detect any defective portionsautomatically.

FIG. 24(A) shows an example for measuring a line width. An actuallyformed pattern Pt2 is scanned in an Ar2 direction to obtain an actualintensity signal of secondary electron Si, wherein a width ws of thissignal continuously exceeding a threshold level SL determined previouslythrough calibration may be measured as a line width of the pattern Pt2.If any line width measured in this way does not fall in a predeterminedrange, then this pattern may be determined to have a defect.

FIG. 24(B) shows an example for measuring a potential contrast of apattern formed on the wafer. In the structure shown in FIG. 8, to theaxially symmetrical electrode 737 disposed between the objective lens729 and the wafer 5 has been applied, for example, a potential of −10Vrelative to a wafer potential of 0V. At that time, an equipotentialsurface of −2V is assumed to be drawn in a shape as indicated by EpS. Itis to be assumed herein that patterns Pt3 and Pt4 are at the potentialsof −4V and 0V respectively. In this case, since a secondary electronemitted from the pattern Pt3 has an upward velocity equivalent to thekinetic energy of 2 eV in the −2V equipotential surface EpS, thesecondary electron overcomes that potential barrier EpS and escapes fromthe equipotential surface Ve as indicated by an orbit Tr1, which wouldbe detected by the detector 761. On the other hand, a secondary electronemitted from the pattern Pt4 can not overcome the potential barrier of−2V and is driven back to the wafer surface as indicated by an orbitTr2, which would not be detected. Accordingly, a detected image for thepattern Pt3 appears to be brighter, while the detected image for thepattern Pt4 appears to be darker. Thus the potential contrast can beobtained. If the brightness and the potential for a detected image havebeen calibrated in advance, the potential of the pattern can be measuredfrom the detected image. Further, based on that potential distribution,the pattern can be evaluated on any defective portions.

Each of the detectors 761 converts the detected secondary electron beaminto an electric signal indicative of an intensity thereof. The electricsignals thus output from respective detectors are, after having beenamplified respectively by the amplifier 763, received by the imageprocessing section 771 of the process control system 77 and convertedinto image data. Since the image processing section 771 is furthersupplied with a scanning signal for deflecting the primary electronbeam, the image processing section 771 can display an image representingthe surface of the wafer W. Comparing this image with the referencepattern allows any defects in the wafer W to be detected.

Further, a line width of the pattern to be evaluated on the wafer W canbe measured in such a manner that firstly a pattern to be evaluated onthe wafer is moved by registration to a position near to the opticalaxis of the primary optical system, secondly a line width evaluationsignal is taken out by line-scanning and then said signal is calibratedappropriately.

Stage Unit and Variation Thereof

Referring to FIGS. 25 to 30, other embodiments of the stage unit will bedescribed. These embodiments of the stage unit relate to an improvementof a structure using a well known hydrostatic bearing. In FIGS. 25 to30, those components corresponding to those of the housing, the stageunit, and the electronic optical system shown in FIGS. 1 or 2 will bedesignated by the same reference numerals with any one of suffixes “d”to “f” added thereto. In some embodiments, common components will bedesignated by the same reference numerals.

Referring to FIG. 25, in a chamber 31 d vacuum-exhausted via a vacuumexhaust pipe 309 d, a stage unit 50 d comprises: a stationary table 51 dof box type (open to above) fixed to a housing 30 d; an X table 54 d ofbox type also, which is operatively mounted in said stationary table 51d so as to be movable in an X-direction (lateral direction in FIG.25(A)); a Y-directionally movable section or a Y table 52 d which isoperatively mounted in said X-directionally movable section or the Xtable 54 d so as to be movable in a Y-direction (lateral direction inFIG. 25(B)); and a turn table 56 d mounted on the Y table 52 d. Thewafer W is detachably held by a well-known holder (not shown) installedon the turn table 56 d. A bottom face 543 d and a side face 544 d of theX table 54 d, each facing to guide faces 511 d and 512 d of thestationary table 51 d, respectively, are provide with a plurality ofhydrostatic bearings 58 d, and owing to an operation of this hydrostaticbearings 58 d, the X table 54 d can be moved in the X-direction (lateraldirection in FIG. 25(A)) while maintaining micro gap against the guidefaces. Further, a bottom face 523 d and a side face 524 d of the Y table52 d, each facing to guide faces 541 d and 542 d of the X table 54 d,respectively, are provide with a plurality of hydrostatic bearings 58 d,and owing to the operation of this hydrostatic bearings 58 d, the Ytable 52 d can be moved in the Y-direction (lateral direction in FIG.25(B)) while maintaining micro gap against the guide faces. In addition,a differential pumping mechanism is arranged around the hydrostaticbearing so that a high pressure gas supplied to the hydrostatic bearingdoes not leak into the vacuum chamber 31 d. This configuration isillustrated in FIG. 26. Around the hydrostatic bearing 58 d are formeddouble grooves 581 d and 582 d 58 d which are always vacuum-pumped by avacuum pipe and a vacuum pump, though not shown. Owing to thesestructures, the X table is operatively supported in the vacuum innon-contact manner so as to be movable in the X-direction, and also theY table is operatively supported in the vacuum in non-contact manner soas to be movable in the Y-direction. These double grooves 581 d and 582d are formed on a surface on which the hydrostatic bearing is providedso as to surround said hydrostatic bearing. The hydrostatic bearing maybe of well-known structure, and the detailed description therefor willbe omitted.

A division plate 525 d is attached onto an upper face of the Y table 52d of the stage unit 50 d, wherein said division plate 525 d overhangs toa great degree approximately horizontally in the +Y direction and the −Ydirection (lateral direction in FIG. 25[B]), so that between an upperface of the X table 54 d and the division plate 525 d may be alwaysprovided a restrictor 526 d with small conductance therebetween. Also, asimilar division plate 545 d is attached onto an upper face of the Xtable 54 d so as to overhang in the +/−X direction (lateral direction inFIG. 25[A]), so that a restrictor 546 d may be constantly formed betweenan upper face of a stationary table 51 d and the division plate 545 d.

In this way, since the restrictor 526 d and 546 d are constantly formedwherever the turn table 56 d may move to, and the restrictors 526 d and546 d can prevent the movement of a discharged gas even if a gas isdischarged or leaked along the guide face 511 d, 512 d, 541 d or 542 dupon movement of the X table or the Y table, a pressure increase can besignificantly controlled to low level in a space G1 adjacent to thewafer to which the charged particle beam is to be irradiated.

Since the grooves for differential pumping formed surrounding thehydrostatic bearings 58 d work for evacuating, therefore in a case wherethe restrictor 526 d and 546 d have been formed, the discharged gas fromthe guiding faces is mainly evacuated by those differential pumpingsections. Owing to this, the pressure in those spaces G2 and G3 withinthe stage are kept to be higher level than the pressure within thechamber 31 d. Accordingly, if there are more portions provided forvacuum-pumping the spaces G2 and G3 in addition to the evacuatinggrooves 581 d and 582 d, the pressure within the spaces G2 and G3 can bedecreased, and the pressure rise of the space G1 in the vicinity of thewafer can be controlled to be further low. For this purpose, evacuatingchannels 517 d and 547 d are provided. The evacuating channel 517 dextends through the stationary table and the housing to communicate withan outside of the housing. On the other hand, the evacuating channel 547d is formed in the X table 54 d and opened in an under face thereof.

It is to be noted that though arranging the division plates 545 d and525 d might cause a problem requiring the chamber 31 d to be extended soas not to interfere with the division plates, this can be improved byemploying those division plates of stretchable material or structure.There may be suggested one embodiment in this regard, which employs thedivision plates made of rubber or in a form of bellows, and the endsportions thereof in the direction of movement are fixedly securedrespectively, so that each end of the division plate 525 d is secured tothe X table 54 d and that of the division plate 545 d to an inner wallof the housing 30 d.

FIG. 27 shows another embodiment of the stage unit and other unitssurrounding the optical column.

In this embodiment, a cylindrical divider 91 e is disposed surrounding atip portion of an optical column 701 d or an electron beam irradiatingsection 702 d, so that a restrictor may be produced between an upperface of the wafer W and the cylindrical divider 91 e. In suchconfiguration, even if the gas is desorbed from the XY stage to increasethe pressure within the chamber 31 d, since a space G5 within thedivider has been isolated by the divider 91 e and exhausted with avacuum pipe 703 d, there could be generated a pressure deference betweenthe pressure in the chamber 31 d and that in the space G5 within thedivider, thus to control the pressure rise in the space G5 within thedivider to be low. Preferably, the gap between the divider 91 e and thewafer surface should be approximately some ten μm to some mm, dependingon the pressure levels to be maintained within the chamber 31 d and inthe surrounding of the irradiating section 702 d. It is to be understoodthat the interior of the divider 91 e is made to communicate with thevacuum pipe by the known method.

On the other hand, the charged particle beam irradiation apparatus orthe electronic optical system may sometimes apply a high voltage ofabout some kV to the wafer W, and so it is feared that any conductivematerials located adjacent to the wafer could cause an electricdischarge. In this case, the divider 91 e made of insulating materialsuch as ceramic may be used in order to prevent any discharge betweenthe wafer W and the divider 91 e.

It is to be noted that a ring member 561 e arranged so as to surroundthe wafer W (sample) is a plate-like adjusting part fixedly attached toa holder (not shown) mounted on the turn table 56 d and is set to havethe same height with the wafer so that a micro gap G6 may be formedthroughout a full circle of the tip portion of the divider 91 e even ina case of the charged particle beam being irradiated against an edgeportion of the sample such as the wafer. Thereby, whichever location onthe wafer W may be irradiated by the charged particle beam, the constantmicro gap G6 can be always formed in the tip portion of the divider 91 eso as to maintain the pressure stable in the space G5 surrounding theoptical column tip portion.

FIG. 28 shows another embodiment in which a differential pumping systemis provided on a tip portion of the optical column.

A division member 91 f having a differential pumping structureintegrated therein is arranged so as to surround the electron beamirradiating section 702 d of the optical column 701 d. The divisionmember 91 f is cylindrical in shape and has a circular channel 911 fformed inside thereof and an evacuating path 912 f extending upwardlyfrom said circular channel 911 f. Said evacuating path 912 f isconnected to a vacuum pipe 914 f via an inner space 913 f. A micro spaceas narrow as some ten μm to some mm is formed between a lower end of thedivision member 91 f and the upper face of the Wafer W.

With such configuration as described above, even if the gas isdischarged from the stage in association with the movement of the stageresulting in an increase of the pressure within the chamber 31 d, andeventually is to possibly flow into the space of the tip portion or thecharged particle beam irradiating section, that is, the electron beamirradiating section 702 d, the gas is prevented from flowing into theelectron beam irradiating section by the division member 91 f, which hasreduced the gap between the wafer W and itself so as to make theconductance very low, thus to reduce the flow-in rate. Further, sinceany gas that has flown into is allowed to be exhausted through thecircular channel 911 f to the vacuum pipe 914 f, there will be almost nogas remained to flow into the space G5 surrounding the electron beamirradiating section 702 d, and accordingly the pressure of the spacesurrounding the electron beam irradiating section 702 d can bemaintained to be a desired high vacuum level.

FIG. 29 shows still another embodiment in which a differential pumpingsystem is provided on a tip portion of the optical column.

A division member 91 g is arranged so as to surround the electron beamirradiating section 702 d in the chamber 31 d and accordingly to isolatethe electron beam irradiating section 702 d from the chamber 31 d. Thisdivision member 91 g is coupled at a central portion thereof 911 g to arefrigerating machine 913 g via a support member 912 g made of materialof high thermal conductivity such as copper or aluminum, and is kept ascool as −100° C. to −200° C. A part 914 g of the division member 91 g isprovided for blocking a thermal conduction between the cooled centralportion 911 g and the optical column and is made of material of lowthermal conductivity such as ceramic, resin or the like. Further, a part915 g of the division member 91 g is made of insulating material such asceramic or the like and is attached to the lower end of the divisionmember 91 g so as to prevent any electric discharge between the wafer Wand the division member 91 g.

With such configuration as described above, any gas molecules attemptingto flow into the space surrounding the charged particle beam irradiatingsection from the chamber 31 d are blocked by the division member 91 g,and even if there are any molecules successfully flown into the space,they are frozen to be captured on the surface of the division member 91g, thus allowing the pressure in the space surrounding the chargedparticle beam irradiating section 702 d to be kept low. It is to benoted that a variety type of refrigerating machines may be used for therefrigerating machine in this embodiment, for example, a cooling machineusing liquid nitrogen, a He refrigerating machine, a pulse-tube typerefrigerating machine or the like.

FIG. 30 shows still another embodiment including a variation of thestage unit and a structure of the optical column with a division memberinstalled on a tip thereof.

The division plates 545 d and 525 d are respectively arranged on the Xtable and the Y table, similarly to those illustrated in FIG. 25, andthereby, if a holder (not shown) for holding the wafer is moved to anylocations, the space G5 within the stage is separated from the innerspace of the chamber 31 d by those division plates via the restrictions546 d and 526 d. Further, another divider 91 e similar to that asillustrated in FIG. 27 is formed surrounding the electron beamirradiating section 702 d so as to separate a space G5 accommodating theelectron beam irradiating section 702 d therein from the interior of thechamber 31 d with a restriction G6 disposed therebetween. Owing to this,upon movement of the stage, even if the gas having been adsorbed ontothe stage is desorbed into the space G2 to increase the pressure in thisspace, the pressure increase in the chamber 31 d is kept to be low, andthe pressure increase in the space G5 is also kept to be much lower.This allows the pressure in the space G5 for irradiating the electronbeam to be maintained at low level. Alternatively, employing thedivision member 91 f having the differential pumping mechanismintegrated therein as shown in FIG. 28, or the division member 91 gcooled with the refrigerating machine as shown in FIG. 29 allows thespace G5 to be maintained stably with further lowered pressure.

FIG. 31 shows still another embodiment of the stage unit and thedifferential pumping system. Since a general configuration of thisembodiment is different from those shown in FIGS. 25 to 30, thosecorresponding components are designated by the same reference numeralswith a suffix “h” added thereto.

A pedestal 511 h of the fixed table 51 h of the stage device 50 h isfixedly mounted on a bottom wall of the housing 30 h, and a Y table 52 hmovable in the Y direction (the vertical direction on paper in FIG. 31)is disposed on the pedestal 511 h. Convex portions 522 h and 523 h areformed on opposite sides (the left and the right sides in FIG. 31) ofthe Y table 52 h respectively, each of which projects into a concavegroove formed on a side facing to the Y table in either of a pair of Ydirectional guides 512 h and 513 h mounted on the pedestal 511 h. Theconcave groove extends approximately along the full length of the Ydirectional guide in the Y direction (the vertical direction on paper inFIG. 31). A top, a bottom and a side faces of respective convex portionsprotruding into the grooves are provided with known hydrostatic bearings58 h respectively, through which a high-pressure gas is blown out andthereby the Y table 52 h is supported by the Y directional guides 512 hand 513 h in non-contact manner so as to be movable smoothlyreciprocating in the Y direction. Further, a linear motor 514 h of knownstructure is arranged between the pedestal 511 h and the Y table 52 hfor driving the Y table in the Y direction. The Y table is supplied withthe high-pressure gas through a flexible pipe 526 h for supplying ahigh-pressure gas, and the high-pressure gas is further supplied to theabove-described hydrostatic bearings 58 h though a gas passage (notshown) formed within the Y table. The high-pressure gas supplied to thehydrostatic bearings blows out into a gap of some microns to some tenmicrons formed respectively between the bearings and the opposing guideplanes of the Y directional guide so as to position the Y tableaccurately with respect to the guide planes in the X and Z directions(up and down directions in FIG. 31).

The X table 54 h is disposed on the Y table so as to be movable in the Xdirection (the lateral direction in FIG. 31). A pair of X directionalguides 522 h and 523 h (only 522 h is illustrated) with the samestructure as of the Y directional guides 512 h and 513 h is arranged onthe Y table 52 h with the X table 54 h sandwiched therebetween. Concavegrooves are also formed in the X directional guides on the sides facingto the X table and convex portions are formed on opposite sides of the Xtable (sides facing to the X directional guides). The concave grooveextends approximately along the full length of the X directional guide.A top, a bottom and a side faces of respective convex portions of the Xtable 54 h protruding into the concave grooves are provided withhydrostatic bearings (not shown) similar to those hydrostatic bearings58 h in the similar arrangements. A linear motor 524 h of knownconfiguration is disposed between the Y table 52 h and the X table 54 hso as to drive the X table in the X direction. Further, the X table 54 his supplied with a high-pressure gas through a flexible pipe 546 h, andthus the high-pressure gas is supplied to the hydrostatic bearings. TheX table 54 h is supported highly precisely with respect to the Ydirectional guide in a non-contact manner by way of said high-pressuregas blowing out from the hydrostatic bearings to the guide planes of theX directional guides. The vacuum chamber 31 h is evacuated throughvacuum pipes 309 h, 518 h and 519 h coupled to a vacuum pump of knownstructure. Those pipes 518 h and 519 h pass through the fixed table 51 hto the top surface thereof to open their inlet sides (inner side of thevacuum chamber) in the proximity of the locations to which thehigh-pressure gas is ejected from the stage device, so that the pressurein the vacuum chamber may be prevented to the utmost from rising up bythe blown-out gas from the hydrostatic bearings.

A differential pumping mechanism 92 h is arranged so as to surround thetip portion of the optical column 701 h or the charged particles beamirradiating section 702 h, so that the pressure in a charged particlesbeam irradiation space G5 can be controlled to be sufficiently low evenif there exists high pressure in the vacuum chamber 31 h. That is, anannular member 921 h of the differential pumping mechanism 92 h mountedaround the charged particle beam irradiating section 702 h is positionedwith respect to the housing 30 h so that a micro gap (in a range of somemicrons to some-hundred microns) G7 can be formed between the lower facethereof (the surface facing to the wafer) and the wafer, and an annulargroove 922 h is formed in the lower face thereof. The annular groove 922h is coupled to a vacuum pump or the like, though not shown, through anevacuating pipe 923 h. Accordingly, the micro gap g5 can be exhaustedthrough the annular groove 922 h and the evacuating pipe 923 h, and ifany gaseous molecules from the chamber 31 h attempt to enter the spaceG5 circumscribed by the annular member 921 h, they may be exhausted.Thereby, the pressure within the charged particle beam irradiation spaceG5 can be maintained to be low and thus the charged particle beam can beirradiated without any troubles. The annular groove 922 h may be madedoubled or tripled, depending on the pressure in the chamber and thepressure within the charged particle beam irradiation space G5.

Typically, dry nitrogen is used as the high-pressure gas to be suppliedto the hydrostatic bearings. If available, however, a much higher-purityinert gas should be preferably used instead. This is because anyimpurities, such as water contents, oil and fat contents or the like,included in the gas could stick on the inner surface of the housingdefining the vacuum chamber or on the surfaces of the stage componentsleading to the deterioration in vacuum level, or could stick on thesample surface leading to the deterioration in vacuum level in thecharged particle beam irradiation space.

It should be appreciated that though typically the wafer is not placeddirectly on the X table, but may be placed on a sample table having afunction to detachably carry the sample and/or a function to make a finetuning of the position of the sample relative to the stage device 50, anexplanation therefor is omitted in the above description for simplicitydue to the reason that the presence and structure of the sample tablehas no concern with the principal concept of the present invention.

Since a stage mechanism of a hydrostatic bearing used in the atmosphericpressure can be used in the above-described charged particle beamapparatus mostly as it is, a high precision stage having an equivalentlevel of precision to those of the stage of high-precision adapted to beused in the atmospheric pressure, which is typically used in an exposingapparatus or the likes, may be accomplished for an XY stage to be usedin a charged particle beam apparatus with equivalent cost and size.

It should be also appreciated that in the above description, thestructure and arrangement of the hydrostatic guide and the actuator (thelinear motor) have been explained only as an example, and anyhydrostatic guides and actuators usable in the atmospheric pressure maybe applicable.

FIG. 32 shows an example of numeric values representative of thedimensions of the annular grooves 922 formed in the annular member 921of the differential pumping mechanism. In this example, a doubledstructure of annular grooves 922 h and 922 h′ which are separated fromeach other in the radial direction is provided.

The flow rate of the high-pressure gas supplied to the hydrostaticbearing is typically in the order of about 20 L/min (in the conversioninto the atmospheric pressure). Assuming that the vacuum chamber C isevacuated by a dry pump having a function of pumping speed of 20000L/min through a vacuum pipe with an inner diameter of 50 mm and a lengthof 2 m, the pressure in the vacuum chamber will be about 160 Pa (about1.2 Torr). At that time, with the applied size of the annular member 921h, the annular groove and others of the differential pumping mechanismas illustrated in FIG. 32, the pressure within the charged particlesbeam irradiation space G5 can be controlled to be 10⁻⁴ Pa (10⁻⁶ Torr).

FIG. 33 shows a vacuum chamber 31 h defined by the housing 30 h and aevacuating circuit 93 for the differential pumping mechanism. The vacuumchamber 31 h is connected to a dry vacuum pump 932 via vacuum pipes 931a and 931 b of the evacuating circuit 93. An annular groove 922 h of adifferential pumping mechanism 92 h is connected with an ultra-highvacuum pump or a turbo molecular pump 933 via a vacuum pipe 931 cconnected to an exhaust port 923 h. Further, the interior of a opticalcolumn 701 h is connected with a turbo molecular pump 934 via a vacuumpipe 931 d connected to an exhaust port 903. Those turbo molecular pumps933, 934 are connected to the dry vacuum pump 932 through vacuum pipes931 e, 931 f. (In FIG. 33, the single dry vacuum pump has been used toserve both as a roughing vacuum pump of the turbo molecular pump and asa pump for vacuum pumping of the vacuum chamber, but alternativelymultiple dry vacuum pumps of separate systems may be employed forpumping, depending on the flow rate of the high-pressure gas supplied tothe hydrostatic bearings of the XY stage, the volume and inner surfacearea of the vacuum chamber and the inner diameter and length of thevacuum pipes.)

A high-purity inert gas (N₂ gas, Ar gas or the like) is supplied to ahydrostatic bearing of the stage device 50 h through flexible pipes 526h, 546 h. Those gaseous molecules blown out of the hydrostatic bearingare diffused into the vacuum chamber and evacuated by the dry vacuumpump 932 through exhaust ports 309 h, 518 h and 519 h. Further, thosegaseous molecules having flown into the differential pumping mechanismand/or the charged particles beam irradiation space are sucked from theannular groove 922 h or the tip portion of the optical column 701 h andexhausted through the exhaust ports 923 h and 703 h by the turbomolecular pumps 933 and 934, and then those gaseous molecules, afterhaving been exhausted by the turbo molecular pumps, are furtherexhausted by the dry vacuum pump 932. In this way, the high-purity inertgas supplied to the hydrostatic bearing is collected into the dry vacuumpump and then exhausted away.

On the other hand, the exhaust port of the dry vacuum pump 932 isconnected to a compressor 935 via a pipe 931 g, and an exhaust port ofthe compressor 935 is connected to flexible pipes 546 h and 526 h viapipes 931 h, 931 i and 931 k and regulators 936 and 937. With thisstructure, the high-purity inert gas exhausted from the dry vacuum pump932 is compressed again by the compressor 935 and then the gas, afterbeing regulated to an appropriate pressure by regulators 936 and 937, issupplied again to the hydrostatic bearings of the stage device.

In this regard, since the gas to be supplied to the hydrostatic bearingsis required to be as highly purified as possible in order not to haveany water contents or oil and fat contents included therein, asdescribed above, the turbo molecular pump, the dry pump and thecompressor are all required to have such structures that they preventany water contents or oil and fat contents from entering the gas flowpath. It is also considered effective that a cold trap, a filter 938 orthe like is provided in the course of the outlet side piping 931 h ofthe compressor so as to trap the impurities such as water contents oroil and fat contents, if any, included in the circulating gas and toprevent them from being supplied to the hydrostatic bearings.

This may allow the high purity inert gas to be circulated and reused,and thus allows the high-purity inert gas to be saved, while the inertgas would not remain desorbed into a room where the present apparatus isinstalled, thereby eliminating a fear that any accidents such assuffocation or the like would be caused by the inert gas.

A circulation piping system is connected to a high-purity inert gassupply source 939, which serves both to fill up with the high-purityinert gas all of the circulation systems including the vacuum chamber C,the vacuum pipes 931 a to 931 e, and the pipes in compression side 931 fto 9311, prior to the starting of the gas circulation, and to supply adeficiency of gas if the flow rate of the circulation gas decreases bysome reason. Further, if the dry vacuum pump 932 is further providedwith a function for compressing up to the atmospheric pressure or more,it may be employed as a single pump so as to serve both as the dryvacuum pump 932 and the compressor 935.

As the ultra-high vacuum pump to be used for evacuating the opticalcolumn, other pumps including an ion pump and a getter pump may be usedinstead of the turbo molecular pump. It should be appreciated that ifthese pumps of an accumulating type is used, a circulating piping systemmay not be provided for the optical column. Further, instead of the dryvacuum pump, a dry pump of other type, for example, a dry pump ofdiaphragm type may be used.

Alternative Embodiment of Electron Beam Apparatus

FIGS. 34 to 37 show an alternative embodiment of the electron opticalapparatus or the electron beam apparatus designated generally byreference numeral 70 i. In these drawings, the same components as thosein the electron beam apparatus shown in FIG. 8 are designatedrespectively by the same reference numerals and detailed explanations onthe structure and function thereof will be omitted. Besides, componentsdifferent from those in FIG. 8 are designated respectively by the samereference numerals, each added with a suffix “i”. Further, in thefollowing description of each of the embodiments for the case with amulti-aperture plate included in a first and a second optical systems,since the relationship between the first and the second multi-apertureplates is same as that illustrated in FIG. 9, therefore an illustrationand an explanation therefor will be omitted.

In the present embodiment, a configuration of an electron beam apparatusis same as that of the electronic optical apparatus shown in FIG. 8,with the exception that a secondary optical system thereof 74 i only hasa single lens and that a detection system thereof 76 i comprises apattern memory 772 connected to an image data processing section 771 ofa process control system 77 i.

In this apparatus, secondary electron images are detected by a set ofdetectors 761 of the detection system 76 i disposed behind apertures7451 of a multi-aperture plate 745 of the secondary optical system 74 iwithout any cross talks with respect to one another, and then formedinto images in the image data processing section 771 that is an imageforming unit. Further, an image for a sample pattern is formed frompattern data and is stored separately in the pattern memory 772, andthereby an image comparing circuit attached to the image data processingsection 771 makes a comparison of the pattern image with an image formedfrom the secondary electron images to classify a defect into any one ofa classification group consisting of short-circuit, disconnection,convex, chipping, pinhole and isolation.

Further, upon measuring a potential of a pattern on a wafer W, apotential lower than that in a surface of the wafer is applied to anaxially symmetric electrode 737 to select the secondary electrons fromthe sample or wafer W based on their energies such that some arepermitted to pass through to an objective lens 729 side and some aredriven back onto the wafer W side thus to measure a voltage of thepattern. This allows more secondary electrons originated from a patternhaving a lower potential to be detected and fewer secondary electronsoriginated from a pattern having a higher potential to be detected, andthereby allows the potential of the pattern on the sample to be measuredbased on a quantity of the detected secondary electrons being large orsmall.

For example, it is assumed that an equipotential surface of 0V has sucha profile around the electrode 737 as illustrated in FIG. 35, when avoltage of −10V is applied to said electrode 737. In that case, thesecondary electron emitted from the pattern having the potential of −2Vwith the given energy of 0V can run over the potential barrier of 0Vthus to be detected, because that secondary electron should still hasthe energy retained at the level of 1 eV at the equipotential surface of0 eV, while on the other hand, the secondary electron emitted from thepattern having the potential of +2V with the given energy of 0 eV isonly permitted to go up to the equipotential surface of 2 eV, whichforces the secondary electron to return back toward the sample and thesecondary electron would not be anyhow detected. Accordingly, the imagefor the pattern of −2V is formed to be brighter, while the image for thepattern of 2V is formed to be darker. Thus the potential contrast may bemeasured.

Further, when a potential measurement of high time resolution is to beperformed, a pulse voltage may be applied to a blanking deflector 731 todeflect the beam and thereby to block said beam by a blanking knife edge734 so as to form it into a multi-beam in the form of short pulses,thereby accomplishing the above-described measurement.

For example, if such pulse voltages as illustrated respectively by [A]and [B] of FIG. 36 are applied to electrodes of the blanking deflector731 disposed in the left and the right sides with respect thereto, thensuch a pulsed beam current as illustrated by [C] of FIG. 36 would beentered onto the wafer. Accordingly, if the pulsed electron beam isentered to the pattern and the secondary electrons emitted at that timeare detected, the potential of the pattern can be measured with the timeresolution having said pulse width. It is to be noted that those dottedlines between the blanking deflector 731 and the blanking knife edge 732in the drawing designate electron beam orbits at the time of blanking.

An inspection procedure by using said electron beam apparatus of thepresent invention will now be described.

FIG. 37 shows an example of the inspection procedure according to thepresent invention. A wafer 11 subject to an inspection is taken out of awafer cassette (1) and then pre-aligned, while at the same time a wafernumber reader, though not shown, reads out a wafer number having beenformed on this wafer (2). The wafer number is unique to an individualwafer. The read-out wafer number is used as a key to read out a recipecorresponding to this wafer (3), said recipe having been registered inadvance. The recipe includes the inspection procedure and/or theinspection condition defined for this wafer.

Subsequent operations may be performed automatically orsemi-automatically according to the read-out recipe. After the wafernumber having been read-in, the wafer W is transferred and mounted ontoan XY stage in a sample chamber held into a vacuum (4). The wafer Wloaded on the XY stage is aligned by the primary and the secondaryoptical systems installed within the sample chamber (5). The alignmentoperation may be performed in such a manner that an enlarged image ofthe alignment pattern formed on the wafer W is compared with a referenceimage registered in advance for the alignment in association with therecipe and then a stage position coordinate is corrected such that thealignment image can be superposed exactly on the reference image. Afterthe alignment, a wafer image (an inspection pattern image) correspondingto this wafer is read out and indicated on a display (6). The waferimage shows a required inspection point and a history for this wafer.

After the wafer image having been indicated, an operator specifies apoint corresponding to a position desired to be inspected among theinspection points shown on the wafer image (7). Once the inspectionpoint is specified, the stage moves and brings the wafer W subject tothe inspection to such a location that the specified inspection pointthereon may be positioned directly below the electron beam (8). Afterthis movement, the scanning electron beam is irradiated onto thespecified inspection point, and an image for the purpose of positioningwith a relatively low magnification is formed thereon. Then, similarlyto the aligning procedure, the formed image is compared with a referenceimage corresponding to the specified inspection point, which has beenregistered in advance for positioning, and a precise positioning isperformed so that the formed image may be superposed exactly on thereference image (9). The positioning may be accomplished by, forexample, a fine-adjustment of the region to be scanned by the electronbeam.

If appropriately positioned, the wafer should be located such that theregion to be inspected is in an approximately central location of thescreen, that is, a location directly below the electron beam. In thisstate, an image in the inspection region to be used for an inspectionwith a high magnification may be formed (10). The image to be used forthe inspection is compared with a reference image corresponding to thisregion to be inspected, which has been registered in advance for theinspection in association with the recipe, and then a different portionbetween those two images is detected (11). The different portion isconsidered as a pattern defect. The pattern defect may be classifiedinto such defect groups including at least short-circuit, disconnection,convex, chipping, pinhole and isolation (12).

Subsequently, the convex and the isolation defects are classifiedaccording to the size, in which a distance to an adjacent pattern isdefined by a unit representing a minimum space and a subtending length(a length of a shadow of a defect projected to a pattern) by a unitrepresenting a minimum pattern width. On the other hand, the pinhole andthe chipping defects are classified according to the size, in which awidth of a pattern including either of said defects is used as a unitdefining the size in the width direction and a minimum pattern width isused as a unit in the longitudinal direction (13). It is to be notedthat the minimum pattern width and the minimum space are values to bedefined based on a pattern design rule for the device subject to theinspection and these values should have been registered prior to theinspection.

After the defect determination and the classification thereof regardingto the specified inspection point having been completed, theclassification result is stored in the inspection database while beingused to overwrite the specified inspection point on the wafer image.Thus the inspection procedure for one location comes to the end asdescribed above.

If there are remaining any inspection locations, a subsequent inspectionpoint may be specified on the wafer image, and the operations followingto the step of specifying the inspection point in FIG. 37 may berepeated. After full range of inspection on said wafer having beenfinished, a density and/or a yield for a total defect, for eachclassified defect, and for each defect distinguished by size iscalculated for each chip or wafer (14). The calculation of the yield maybe executed by using a critical rate table of defect size for therespective defect types registered in advance. The critical rate tableof defect size has been prepared to correlate each of the defectsincluding the convex, chipping, pinhole and isolation, which have beenclassified by size, with each unique critical rate. These calculationresults may be stored in the inspection database together with theinspection result (14), and output to be used at any times as desired(15).

If there remains any wafers to be measured in a wafer cassette, asubsequent wafer is taken out of the wafer cassette and then inspectedaccording to the procedure shown in FIG. 37. The density and the yieldfor a plurality of wafer are also calculated similarly to the case ofthe wafer as described above.

It is to be appreciated that if the electron beam apparatus is furtherequipped with additional analyzing functions by means of, for example, acharacteristic X-ray analyzer or an Auger electron analyzer, it maybecome possible to obtain analytic data of the inspection point such asdata including a defective composition in addition to the classificationin the defect determination based on the inspection image.

Further Alternative Embodiment of Electron Beam Apparatus

FIGS. 38 and 39 show an alternative embodiment of the electron beamapparatus designated generally by reference numeral 70 j. In FIGS. 38and 39, the same components as those in the electron beam apparatusshown in FIG. 8 are designated respectively by the same referencenumerals and detailed explanations on the structure and function thereofwill be omitted. Besides, components different from but similar to thosein FIG. 8 are designated respectively by the same reference numerals,each added with a suffix “j”.

An electron beam apparatus according to this embodiment is same as theelectron optical apparatus as shown in FIG. 8 with the exception that anaperture plate 735 defining an aperture is located at a point P1 where acrossover of a primary optical system 72 j is formed, that an apertureplate 747 defining an aperture is located at a point P4 where acrossover of a secondary optical system 74 j is formed, and that thesecondary optical system 74 j comprises an electrostatic deflector 746.

In the electron beam apparatus of the present embodiment, a plurality ofsecondary electron beams emitted from respective irradiation spots on awafer W is guided to a detector through the secondary optical system 74j. In a stage prior to a magnifying lens 743, the electrostaticdeflector 746 is arranged so as to function as an axially aligningdevice for the magnifying lens 743. Further, the aperture plate 747defining the aperture is arranged at the location P4 where the secondcrossover image is formed so as to obtain the resolution of the secondoptical system.

Herein, any cross talks among a plurality of beams may be avoided bymaking a spacing between a plurality of primary electron beams begreater than the resolution of the secondary optical system as convertedinto the value on the wafer surface. The spacing between the irradiationspots is scanned by said electrostatic deflector 746. This allows animage to be created in the same principle as of the SEM and also with athroughput proportional to the number of beams. Since chromaticaberration can be reduced by controlling an angle of deflection of theelectrostatic deflector 746 to a value proximal to −½ of an angle ofelectromagnetic deflection by an ExB separator 726, therefore thedeflection would not increase the beam diameter excessively.

Each of detecting elements of a detector 761 is connected via each ofamplifiers 763 to an image data processing section 771 of a processcontrol system 77 for converting a detection signal to the image data.Since the image data processing section 771 is supplied with the samescanning signal as that given to a deflector 733 for deflecting theprimary electron beam, the image data processing section 771 can figureout an image representative of the scanned surface of the wafer W fromthe detection signal obtained during the beam scanning.

As can be seen obviously from FIG. 38, since a portion in the opticalpath common to the primary optical system and the secondary opticalsystem is the portion from the ExB separator 726 through an objectivelens 729 up to the wafer W, the number of common optical parts has beensuccessfully decreased. Owing to this, even if the lens condition forthe objective lens 729 was matched to the primary electron beam, afocusing condition for the secondary electron beam can be adjusted byusing the magnifying lenses 741 and 743. The latter, the magnifying lens743 is to magnify an angle θ1 made by an orbit of the secondary electronand the optical axis OA₂ to θ2.

In addition, although the axial alignment with respect to the objectivelens 729 is performed favorably to the primary electron beams byapplying an axial aligning power supply voltage onto the deflector 728in superposition to its due voltage, the axial mismatch of the secondaryelectron beam due to the axial alignment favorable to the primaryelectron beam can be compensated for by using the axial aligner for thesecondary optical system or the deflector 746.

As for the aperture plate defining the aperture, two aperture plates hasbeen employed, one of which is the aperture plate 735 for passing onlythe primary electron beam therethrough disposed at the location P1 wherethe first cross over image is formed, and the other of which is anotheraperture plate 747 for passing only the secondary electron beamtherethrough disposed at the location P4 where the second cross overimage is formed, thereby allowing an optimal aperture diameter to beselected individually. Employing a size of an aperture of the objectivelens 729 sufficiently greater than the diameter of the cross over hereinand zooming the objective lenses 721 and 725 so as to make the crossover size variable at the position of the objective lens 729 can make anangular aperture selectable. This allows the angular aperture to beadjusted to a desired optimal value within a range determined by thetrade-off between the low aberration and the high beam current by onlyusing an electric signal without exchanging apertures.

As for the location of the aperture of the secondary optical system,such a condition should be satisfied that the secondary electron imagecould be focused on the detector 761 by the magnifying lenses 741 and743. Then, the aperture is to be moved along the optical axis OA₂ untilthe location where every secondary electron beam may have the sameintensity when the wafer with the inspected surface having a uniformemission characteristic has been used, and at that location, theaperture of the secondary optical system should be fixed. This positionis the location in the optical axis direction where the principal rayfrom the wafer would cross the optical axis as illustrated.

In a pattern defect inspection method for a wafer W by way of thepattern matching, a control section which is not shown but has beenprovided for controlling the electron beam apparatus executes acomparative matching between a secondary electron beam reference imageof a wafer having no defect which has been stored in a memory thereof inadvance and an actually detected secondary electron beam image so as tocalculate a similarity between those two images. For example, if thecalculated similarity is not greater than a threshold, it is determinedthat “a defect exists” and if the calculated similarity is greater thanthe threshold, it is determined that “no defect exists”. At this stage,the detected image may be displayed on a CRT, though not shown. Thereby,an operator can make a final confirmation and thus evaluate whether thewafer W has actually a defect or not. Further, the images may becompared to see a matching in segment by segment base so as to detectautomatically the segment including the defect. In that case, preferablyan enlarged image representing the defective segment should be displayedon the CRT.

Still further, for a wafer having a number of same dice, the detectedimages may be compared between the detected dice so as to detect thedefective part without the need for using the reference image asdescribed above. For example, FIG. 39 [A] shows an image Im1 for afirstly detected die and another image Im2 for a secondarily detecteddie. If it is determined that another image for a thirdly detected dieis same as or similar to the first image Im1, then it can be determinedthat the second die image Im2 has a defect in the segment Nt, and thus adefective part can be detected. At this stage, the detected image may bedisplayed on the CRT while marking the segment determined to bedefective.

It is to be noted that to measure a line width of a pattern or apotential contrast of the pattern formed on the wafer, the operation maybe performed in the manner as described in conjunction with FIG. 24, andthe explanation thereof will be omitted.

Referring to FIG. 38, since a blanking deflector 731 has been provided,said deflector 731 may be used to deflect the primary electron beamtoward the aperture at the cross over image formation point in apredetermined cycle so as to permit the beam to pass therethrough for ashort period and to block it for the rest of the period, which will berepeated, then it will be possible to form a bundle of beams having ashort pulse width. If such a beam having a short pulse width is used tomeasure the potential on the wafer as described above, the deviceoperation characteristics can be analyzed with high time resolution.That is, the present electron beam apparatus can be used as what iscalled an EB tester.

Further Alternative Embodiment of Electron Beam Apparatus

FIG. 40 shows an alternative embodiment of the electron opticalapparatus or the electron beam apparatus designated generally byreference numeral 70 k. In FIG. 40, the same components as those in theelectron beam apparatus shown in FIG. 8 are designated respectively bythe same reference numerals and detailed explanations on the structureand function thereof will be omitted. Besides, components different frombut similar to those in FIG. 8 are designated respectively by the samereference numerals, each added with a suffix “k”.

The electron beam apparatus according to the present embodiment is sameas the embodiment of FIG. 8 with the exception that the apparatusfurther comprises a mode determining circuit 775 connected to an imagedata processing section 771 of a process control system 77 k, that saidmode determining circuit 775 is provided with a CPU 776, a memorysection 777 connected to said CPU 776 and an operator console 778, andthat said memory section is connected to respective components in aprimary optical system 72 and a secondary optical system 74.

In the electron beam apparatus of the present embodiment, a secondaryelectron image is formed on one of a plurality of apertures 7451 of asecond multi-aperture plate 745 by magnifying lenses 741 and 743, andthis second electron image is detected by each of detectors 761. Each ofthose detectors 761 converts the detected secondary electron image intoan electric signal representing an intensity thereof. In this way, theelectric signal output from each of the detectors, after having beenamplified by the corresponding amplifier 763, is entered into the imagedata processing section 771 of the process control system 77 k andconverted into an image data in this image data processing section.Since the image data processing section 771 is further supplied with thescanning signal for deflecting the primary electron beam, the image dataprocessing section 771 may display an image representative of thesurface of a sample or a wafer W. By comparing this image with areference pattern allows a defect in the wafer to be detected, andfurther, by moving the pattern to be evaluated on the wafer W to alocation proximal to an optical axis OA₁ of the primary optical system72 by way of registration and then line-scanning this pattern, a linewidth evaluation signal for the pattern formed on the top surface of thesample can be extracted, which is further calibrated appropriately so asto measure the line width of the pattern.

In the case for evaluating a wafer having a pattern with a minimum linewidth of 0.1 μm, if there are some evaluation modes available for theelectron beam apparatus, including a mode using a pixel size of 0.2 μmfor performing an evaluation with high throughput, another mode usingthe pixel size of 0.1 μm for performing an evaluation with higherprecision but the throughput deteriorated to one-quarter of that by thefirst mode, and further the other mode using the pixel size of 0.05 μmfor allowing an evaluation with much higher precision but the throughputfurther deteriorated to one-quarter of that by said another mode, thensuch electron beam apparatus may advantageously works for many uses.

On the other hand, when the pixel size is changed, the beam size andthus a scanning dimension need to change in association with the changein pixel size. To change the scanning dimension, it is only required tochange a voltage to be applied to the deflector. In contrast, to changethe beam size, it is required to change many parameters.

In FIG. 40, the primary electron beam, after having passed through aplurality of apertures 7231 of the multi-aperture plate 723 is forcusedby a reduction lens 725 and an objective lens 729. Accordingly,conditions for the reduction lens 725 and the objective lens 729 may bedetermined and stored in the memory section in advance, so that thezooming effect from those two lenses may be used to change a reductionratio to form a beam in a size suitable for each of the pixel sizes of0.05 μm, 0.1 μm and 0.2 μm, and the appropriate condition may beextracted and established at each time when the mode is changed. Fromthe viewpoint of the secondary optical system, since the objective lensis determined by the condition for the primary optical system, theabove-described method is not applicable to the secondary opticalsystem. In the secondary optical system, the lens condition may bedetermined such that the secondary electrons or a principal ray emittedfrom the sample in a right angle with respect to the surface thereof canbe entered exactly into each of the apertures 7451 of the secondmulti-aperture plate 745 of the secondary optical system by at leastone-step of lens arranged downstream to an ExB separator 727. These lensconditions and axial aligning conditions for each of those three modesmay be stored in the memory section 777 of the mode determining circuit.Then, the input from the operator console 778 may control the CPU 776 toextract the conditions and to reset the values appropriately at eachtime when the mode is changed.

FIG. 41 shows an embodiment in which a mode determining circuit similarto that in preceding embodiment is applied to an electron beam apparatusof the scanning type for irradiating a single electron beam, which isdesignated generally by reference numeral 70 m. In FIG. 41, componentscorresponding to those in the preceding FIG. 40 are designated by thesame reference numerals, each added with a suffix “m”.

In this embodiment, since a condenser lens 721 m has substantially thesame structure as that of an objective lens 729 m, therefore thecondenser lens is representatively explained in detail.

The condenser lens 721 m, which is an electrostatic axially symmetriclens, comprises a main body 7210 made of ceramic. This main body 7210 isformed to be annular in plan view to define a circular opening 7211 in acentral portion thereof, and an inner circle side thereof is dividedinto three plate-like sections 7212 to 7214 spaced to one another in alongitudinal direction (the direction along the optical axis) in FIG.41. An outer surface of the ceramic made main body 7210, especially theouter surface of the plate-like sections 7212 to 7214, is coated withmetal coating films 7212′ to 7214′. These coating films 7212′ to 7214′serve as electrodes respectively, in which to the coating films 7212′and 7214′ is applied respectively a voltage having a level approximateto the ground side, while to the central coating film 7213′ is applied apositive or a negative high voltage having a high absolute value throughthe electrode fitting 7215 provided on the main body 7210, thereby toserve as a lens. Such lens is allowed to be of high processing accuracyand to be made smaller in an outer diameter because each element thereofis formed out from a single piece of ceramic by machining and finishingsimultaneously.

In the electron beam apparatus of the above embodiment, since the outerdiameter of the lens can be made smaller, the diameter of the opticalcolumn containing the electron beam apparatus also may be reduced.Therefore, it becomes possible to arrange a plurality of optical columnsfor one piece of sample such as a wafer having a larger diameter. Forexample, the array of four pieces of optical columns in the X directionby two rows in the Y direction, that is, eight optical columns 701 m intotal may be arranged for one piece of sample, as shown in FIG. 42. Inthis arrangement, the distances between optical axes of respectiveoptical systems projected in the X-axis direction are made all equal.Employing such an arrangement can eliminate a not-evaluated region or adoubly evaluated region with several times of mechanical scanning. Then,when the stage (not shown) holding the wafer W is continuously moved inthe Y-direction and each of the optical columns scans in the X directionwith a width of 1.1 mm, then a 8 mm wide region can be evaluated withone time of mechanical scanning. It is to be appreciated that a 50 μmwide region should be doubly evaluated.

The lens conditions and axial aligning conditions for each of the modesmay be measured in advance and stored in the memory section 777belonging to the mode determining circuit 775, and then, an input fromthe operator console 778 controls the CPU 776 to extract the conditionsand reset the values appropriately at each time when the mode ischanged.

Further Alternative Embodiment of Electron Beam Apparatus

FIGS. 43 and 44 show an alternative embodiment of the electronic opticalapparatus or the electron beam apparatus designated generally byreference numeral 70 n. In FIGS. 43 and 44, the same components as thosein the electron beam apparatus shown in FIG. 8 are designatedrespectively by the same reference numerals and detailed explanations onthe structure and function thereof will be omitted. Besides, componentsdifferent from but similar to those in FIG. 8 are designatedrespectively by the same reference numerals, each added with a suffix“n”.

The electron beam apparatus according to the present embodiment is sameas the embodiment of FIG. 8 with the exception that the apparatusfurther comprises a laser interferometer in association with the stageunit and the objective lens, and that an aperture plate is arranged at apoint P1 where a cross over is formed.

FIG. 44 illustrates in detail a specific structure of an electrostaticlens which constitutes an objective lens 729 n shown in FIG. 43. Theobjective lens 729 n is formed into an axially symmetric structurecentering around an optical axis OA₁, wherein only a right half-portionthereof is shown in a sectional view of FIG. 44.

The objective lens 729 may be fabricated in the following manner.Primarily, a metal bar 7299 is embedded into a ceramic material, whichcan be shaped by machining, so as to form a circularly cylindrical part7290. Secondarily, the ceramic material is machined with a lathe inorder to form an upper electrode section 7292, a central electrodesection 7293, a lower electrode section 7294 and an axially symmetricelectrode section 7295. Then, the masking is applied to those portionswhere the surface of the ceramic material is to be exposed forinsulation, and a metal plating is applied to the remaining surfaceportions of the ceramic material by way of electroless plating, therebyforming an upper electrode 7292′, a central electrode 7293′, a lowerelectrode 9294′ and an axially symmetric electrode 7295′.

The upper electrode 7292′ is supplied with a voltage from a lead 7296connected to a top surface thereof. The central electrode 7293′ and thelower electrode 7294′ are supplied with voltages from leads 7297 via apair of metal bars 7299. It is to be noticed that a vacuum sealing isnot necessary to the metal bar 7299. The axisymmetric electrode 7295′ issupplied with a voltage from a lead 7298 connected to a lower facethereof.

A cylindrical part made of ceramic having such a configuration asdescribed above may be fabricated small in size, and then a ceramicmember 7300 having a low coefficient of linear expansion (e.g.,NEXCERAN113 available from Nippon Steel Corporation) is adhered onto theouter side thereof. Then, a planer stationary laser mirror 7301 isfixedly adhered to the outer side of said ceramic member 7300. Thestationary laser mirror 7301 may be formed by polishing a side of theceramic member 7300 subject to the laser beam to be a mirror-surface.

The integration of the stationary laser mirror 7301 into the objectivelens 729 n (fixing by adhesion or integration in structure) makes itpossible that in case of the vibration of the optical system in the X-Yplane direction in addition to the vibration of the stage unit as thematter of course, the laser interferometer measures a displacement ofthe electron beam due to such vibration and the beam position may beaccordingly compensated. That is, even if the objective lens 729 nvibrates in the x-y direction, a variation in relative distance withrespect to the stage 50 n can be measured by the laser interferometer 94and thereby the compensation may be applied to the beam so as to offsetthe variation. In this manner, a relative micro-vibration between theoptical system and the stage can be compensated and thereby an imagedistortion due to the vibration of the optical system can be reduced.

An evaluation such as a defect inspection of a pattern formed on asurface of a wafer W which is a sample is to be accomplished by usingthe electron beam apparatus shown in FIG. 43, an electrostatic deflector733 and a magnetic deflector 728 of a Wien filter or an E×B separator726 should be operated interlockingly and at the same time an X tableand a Y table of a stage unit 50 n are to be moved, so that a pluralityof primary electron beams may scan the surface of the wafer W in theX-direction while continuously moving the wafer W in the Y-direction,thus scanning the overall surface of the wafer W. That is, after thestage unit 50 n having been moved to place the wafer W at a scanningstarting end, the stage unit is moved continuously in the Y-directionwhile controlling a plurality of primary electron beams to scan in theX-direction with an amplitude slightly greater than a distance betweenrespective primary electron beams, Lx (shown in FIG. 9). This means thatthe wafer could have been scanned in the region extending along theY-direction having a width w equivalent to full scanning distance of theplurality of primary electron beams in the X-direction, and a signal inassociation with the scanning in said region would be output from adetector 761.

Subsequently, after the stage unit having been moved in the X-directionby a step equivalent to the width w, the table of the stage unit 50 iscontinuously moved in the Y-direction while controlling the plurality ofprimary electron beams to scan the wafer W in the X-direction by thedistance equivalent to the width w. Thereby, another region of the widthw adjacent to the region having been previously scanned would have beenscanned both in the X- and the Y-directions. After this, the similaroperations may be repeated to scan the overall surface of the wafer W,and the signal obtained as a result of scanning operations from thedetector 761 may be processed so as to evaluate the wafer W.

It is to be appreciated that, preferably, the laser interferometer 94should be employed in order to precisely control the movement of thestage unit 50 n. To achieve this, the X table and the Y table of thestage unit are provided with movable laser mirrors 941, while a laserinterferometer 942 with a built-in laser oscillator 943, a stationarylaser mirror 946 (which may be the same mirror as the reference mirror7301 of FIG. 44) secured fixedly to the objective lens, a reflectionmirror 944 and a dichroic mirror 945 are mounted respectively inappropriate locations on the stationary side as illustrated, so that aposition of the stage can be calculated based on the interferencebetween the light which has followed an optical path from the laseroscillator 943 → the dichroic mirror 945 → the reflection mirror 944 →the stationary laser mirror 946 (7301) → the reflection mirror 944 → thedichroic mirror 945 → the laser interferometer 942 and the light whichhas followed another optical path from the laser oscillator 943 → thedichroic mirror 945 → the stationary laser mirror 941 → the dichroicmirror 945 → the laser interferometer 942.

In the laser interferometer 94 of FIG. 43, the interferometer for eitherone of the X-axis or the Y-axis direction has been illustrated, and theinterferometer for the other direction has been omitted. However, inpractice, the interferometer should be provided for both of the X-axisand the Y-axis directions as a matter of course. For example, as for themovable mirror 941, orthogonal side faces of the X and the Y tables ofthe stage unit may be provided with movable mirrors for the X-axis andfor the Y-axis, respectively.

If the wafer W is a semiconductor wafer, then instead of theabove-described evaluation method, the following method may be taken toevaluate the wafer W. That is, a marker may be arranged at anappropriate location on the surface of the wafer W, such that only theone electron beam among a plurality of primary electron beams, which hasbeen formed by one aperture of a multi-aperture plate 723, may beallowed to scan said marker and an output from the detector at that timeof scanning is extracted to detect the position of the marker. Thereby,a physical relationship between the wafer W and the primary electronbeam can be determined, and therefore, if an orientation of a circuitpattern formed on the surface of the wafer W with respect to the X- andthe Y-directions have been determined in advance, a plurality of primaryelectron beams could be guided to the correct position to meet saidcircuit pattern and the beams therein could scan the circuit pattern,thereby accomplishing the evaluation of the circuit pattern on the waferW.

Further, the line width of the pattern on the surface of the wafer W canbe measured in such a way that first a pattern to be evaluated on thewafer W is moved by registration to the proximity to the optical axis ofthe primary optical system and the wafer W is line-scanned with theprimary electron beam to detect the secondary electron beam, and then asignal corresponding to this secondary electron beam is detected toextract a signal for evaluating the line width of the circuit pattern onthe surface of the wafer W, which is then calibrated appropriately thusto measure the line width of the pattern on the surface of the wafer W.

FIG. 45 shows an embodiment in which a mode determining circuit having aprinciple similar to that of the above-described embodiment is appliedto an electron beam apparatus of scanning type for irradiating a singleelectron beam, which is designated generally by reference numeral 70 p.In FIG. 45, components corresponding to those in the embodiment of FIG.43 are designated by the same reference numerals, each added with asuffix “p”,

An electron gun 71 p comprises an anode 713 p and a cathode 711 p so asto emit a primary electron beam having a cross over with a diameter ofapproximately 10 microns. Thus emitted, the primary electron beam passesthrough an axial aligning deflectors 731 p, 731 p′ and further throughthe condenser lens 721 p, where being converged, and further passesthrough a deflector 733 p and a Wien filter or an ExB separator 726 p,and thereafter the beam is forcused by an objective lens 729 p so as tobe formed into an image on the proximity to a plurality of circuitpatterns in the shapes of, for example, rectangles formed on a surfaceof a wafer W loaded on a stage unit 50. Deflectors 10 and 40 control theprimary electron beam to scan the wafer W.

Secondary electron beam emitted from the pattern on the wafer W as theresult of the scanning with the primary electron beam is accelerated byan electric field of the objective lens 729 p and deflected by the Wienfilter 726 to deviate from an optical axis OA₁ thus to be separated fromthe primary electron beam. Then, the secondary electron beam is detectedby a secondary electron detector 761 p. The secondary electron detector761 p outputs an electric signal representing an intensity of thesecondary electron beam entered therein. The electric signal output fromthis detector 761 p is input to an image data processing section 771 ofa process control system 77 p after having been amplified by acorresponding amplifier (not shown).

As shown in FIG. 45, the electron gun 71 p, the axial aligningdeflectors 731 p, 731 p′, the condenser lens 721 p, the deflector 733 p,the Wien filter 726 p, the objective lens 729 p and the secondaryelectron beam detector 761 p are all accommodated within an opticalcolumn 701 p having a diameter corresponding to a given area of thewafer W, thus composing a single unit of electron beam scanning anddetection system, which is used to scan the circuit pattern on the waferW. In practice, a plurality of dice has been formed on the surface ofthe wafer W. Other electron beam scanning/detection systems (not shown)each having a similar configuration to the above-described electron beamscanning and detection system is arranged in parallel with the opticalcolumn 701 p so as to be used to scan the same location on a differentdie on the wafer W.

Although the electron beam scanning and detection system operates in thesame manner as in the preceding explanations, what is different is thatthe electric signal output from the secondary electron detection systemof each of the electron beam scanning/detection systems, which isconstructed as one beam/one detector per one optical column, is enteredinto the image data processing section 771 of the process control system77. Then, the image data processing section 771 converts the electricsignal entered from each of the detection systems into a binaryinformation, and further converts this binary information into an imagedata with reference to the electron beam scanning signal. To accomplishthis, a signal waveform having given to the electrostatic deflector 733p is supplied to the image data processing section 771. The image dataobtained for each of the dice formed on the surface of the wafer W iscompared with a reference die pattern while being accumulated in anappropriate memory. This allows a defect to be detected for every one ofthe plurality of die patterns formed on the surface of the wafer W.

It is to be noted that similarly to the above-described embodiments,also in the embodiment shown in FIG. 45, a variety of circuit patternsmay be used as the reference circuit pattern to be used by the imagedata processing section 771 for making a comparison with a specificimage data representing a certain die pattern on the wafer W, and forexample, such image data obtained from the CAD data of the die pattern,to which the scanning has been applied so as to generate said specificimage data, may be used.

The Wien filter or the E×B separator 726 p comprises an electrostaticdeflector 728 p and an electromagnetic deflector 727 p arranged so as tocircumscribe said electrostatic deflector 728 p. As this magneticdeflector 727 p, preferably a permanent magnet made of platinum alloymay be used instead of an electromagnetic coil. This is because applyinga current in a vacuum environment is not adequate. Further, thedeflector 733 p functions both as the axial aligner for aligning thedirection of the primary electron beam with the axis of the objectivelens 729 p and the scanner.

Since the method for fabricating the condenser lens 721 p and theobjective lens 729 p may be same as the method for fabricating thecondenser lens and the objective lens in the embodiment shown in FIG.41, a detailed explanation thereof will be omitted.

As described before, since the condenser lens 721 p and the objectivelens 729 p are fabricated by way of machining the ceramic, it ispossible to process those lenses with high level of precision and toreduce the outer diameters thereof. Accordingly, if the outer diametersof the condenser lens 2 and the objective lens 729 p are reduced to, forexample, not greater than 20 mm, then six or eight electron beamapparatuses can be arranged for one piece of wafer by employing such anarray of the optical column as shown in FIG. 42 in the case of theinspection of the wafer having a diameter of 200 mm with a range forinspection defined by a diameter of 140 mm, the throughput in increasedby 6 or 8 times.

It is to be appreciated that the laser reference reflection mirrors tobe mounted on the objective lens and the stage unit may be fabricatedaccording to the fabrication processes shown in FIG. 46.

In the method, as shown in FIG. 46, primarily SiC ceramic was processedto have a dimension defined by a sectional area of 30 mm×30 mm and alength of 35 cm (STP 1). A laser reflecting surface thereof was groundto be a fine obscured glass like face having a rough but high flatnesssurface (STP 2). Subsequently, a CVD apparatus was used to apply a filmdeposition thereto up to a level to fill in sufficiently a void on thereflecting surface due to a void formed inside thereof and the roughsurface (20 μm thick in one example) (STP4). In that stage, in order tofill in the void and the like efficiently, the mirror was inclined so asto form an angle of approximately 45 degrees between the vertical lineand the reflecting surface and left in this condition for a long timeperiod thus to form the film.

After that, a mirror polishing was applied to the object (STP 6). Sincethe surface prior to the deposition by the CVD was in the fine obscuredglass like condition, even at the time of polishing, there would neveroccur a separation between the main body and the CVD film. After themirror polishing, a multi-layer reflection film or titanium, gold or thelike was used to form a reflecting film (STP 8).

Further Alternative Embodiment of Electron Beam Apparatus

FIG. 47 shows an alternative embodiment of the electronic opticalapparatus or the electron beam apparatus designated generally byreference numeral 70 q. In FIG. 47, the same components as those in theelectron beam apparatus shown in FIG. 43 are designated respectively bythe same reference numerals and detailed explanations on the structureand function thereof will be omitted. Besides, components different frombut similar to those in FIG. 43 are designated respectively by the samereference numerals, each added with a suffix “q”.

The electron beam apparatus according to this embodiment is same as theelectron beam apparatus shown in FIG. 43 with the exception that anaperture plate 747 is disposed at a point P4 in a secondary opticalsystem 74 q where a cross over is formed, that the secondary opticalsystem comprises an electrostatic deflector 746 and that a detectionsystem comprises a control section 78.

In this embodiment, each of the detectors 761 is connected via each ofthe amplifier 763 to an image data processing section 771 of a processcontrol system 77 q for converting a detection signal into an imagedata. Since the image data processing section 771 is supplied with thesame scanning signal as that given to a deflector 733 for deflecting theprimary electron beam, the image data processing section 771 can figureout a secondary electron pattern image for a pattern formed on a wafer Wfrom the detection signal obtained during the beam scanning.

The image data processing section 771 is operatively connected with thecontrol section 780 so as to be capable of performing a datacommunication therebetween. This control section 780 executes anevaluation on the wafer W based on the secondary electron pattern imagegenerated by the image data processing section while controlling andmanaging the whole electron beam apparatus.

The control section 780 is connected with a display section 782 forindicating an evaluation result or the like and an input section 781 forentering a command of an operator. The display section 782 may be madeup of a CRT or a liquid-crystal display and may indicate a defectivepattern, a secondary electron pattern image, the number of defectivelocations and so on.

The wafer W may be placed on a stage unit 50 n. This stage unit isconfigured such that it can move within a horizontal plane in the X andthe Y directions with the wafer W placed thereon in response to thecommand from the control section 78. That is, the stage unit 50 nenables the wafer W to move in the X and the Y directions with respectto the primary and the secondary optical systems. Since a laserinterferometer 94 to be arranged in conjunction with the stage unit andan objective lens has the same structure and function as those of theapparatus shown in FIG. 43, detailed explanations thereof will beomitted.

A laser reflection mirror 941 provided in the form of a movable mirrorrequires to be at least 30 cm long for evaluating a 12-inch wafer W, andto be further longer for the YAW measurement or for aligning an opticalaxis OA₁ of the primary optical system onto a fixed marker or a Faradaycup of the stage device 50 n, being around 40 cm long in most cases. Inthe present embodiment, a base body of such a long laser reflectionmirror 941 is made of highly rigid SiC ceramic without increasing thethickness thereof. If a side face of a top surface member of the stagedevice is formed as the reflection mirror, then the rigidity can befurther improved.

Preferably, a laser reflection mirror 946 provided in the form of areference mirror may be attached to a ring, which is made of ceramichaving a coefficient of linear expansion almost equal to 0 and has beenattached to an outer cylinder of the objective lens 729, in order toavoid an affection from thermal expansion of the optical column. Thisreference mirror 946 may be made of SiC ceramic similarly to the movablemirror 941.

An operation of the electron beam apparatus according to the presentembodiment will now be described. As can be seen obviously from FIG. 47,since a portion in the optical path common to the primary optical systemand the secondary optical system is the portion from an ExB separator727 through the objective lens 729 up to the wafer W, the number ofcommon optical parts has been successfully decreased. Owing to this,even if the lens condition for the objective lens 729 was matched to theprimary electron beam, a focusing condition for the secondary electronbeam can be adjusted by using magnifying lenses 741 and 743. Inaddition, although the axial alignment with respect to the objectivelens 729 is performed favorably to the primary electron beams byapplying an axial aligning power supply voltage onto the deflector 733in superposition to its due voltage, the axial mismatch of the secondaryelectron beam due to the axial alignment favorable to the primaryelectron beam can be compensated for by using the axial aligner for thesecondary optical system or the electrostatic deflector 746.

As for the aperture plates 735, 747 defining numerical apertures, twoaperture plates has been employed, one of which is disposed at thelocation where the first cross over image is formed (an installationpoint of an opening aperture 4) and only the primary electron beampasses therethrough, and the other of which is disposed at the locationwhere the second cross over image is formed (an installation point of anopening aperture 747) and only the secondary electron beam passestherethrough, thereby allowing an optimal aperture diameter to beselected individually. Employing a size of an aperture of the objectivelens 729 sufficiently greater than the diameter of the cross over hereinand zooming the objective lenses 721 and 725 so as to make the crossover size variable at the position of the objective lens 729 can make anangular aperture selectable. This allows the angular aperture to beadjusted to a desired optimal value within a range determined by thetrade-off between the low aberration and the high beam current by onlyusing an electric signal without exchanging apertures.

As for the location of the aperture of the secondary optical system,such a condition should be satisfied that the secondary electron imagecould be focused on the detector 761 by the lenses 741 and 743. Then,the aperture is to be moved along the optical axis (Z) until thelocation where every secondary electron beam may have the same intensitywhen the wafer with the inspected surface having a uniform emissioncharacteristic has been used, and at that location, the aperture of thesecondary optical system should be fixed. This position is the locationin the optical axis direction where the principal ray from the waferwould cross the optical axis as illustrated.

A process for obtaining the secondary electrons is as follows. Theprimary electron beam emitted from the electron gun 71 is focused by thecondenser lens 721 to form a cross over at a point P1. Since, passingthrough a plurality of apertures 7231 of the first multi aperture plate723 on the way to the point P1, the primary electron bean is formed intoa plurality of beams. The plurality of beams is focused on a point P2 bythe reduction lens 725 and further forcused through the objective lens729 to be formed into an image on the wafer W. Thus, on the wafer W, aplurality of irradiation spots each having almost the same intensity isformed by the primary electron beam, and then the secondary electronsare emitted from those irradiation spots respectively. During thisperiod, the electrostatic deflector 733 deflects the primary electronbeam so as to scan a certain region slightly larger than the spacingbetween adjacent two beams. This deflection allows the irradiation spotson the wafer to scan in the beam aligning direction with no region leftnot-scanned.

The multi-beam consisting of the secondary electrons emitted from therespective irradiation spots on the wafer is accelerated by the electricfield of the objective lens 7 and converged to be narrower, and thenreaches to an ExB separator 726, where the multi-beam is deflected by afield (ExB) generated therein into the direction at a specified anglewith respect to the optical axis OA₁ to proceed along the optical axisOA₂ of the secondary optical system 74 q. The secondary electron imageis focused on the point P3 that is closer to the objective lens 729 thanthe point P2. This is because typically each of the secondary electronbeams only has an energy of some eV, while each of the primary electronbeams having the energy of, for example, 500 eV on the wafer. Themulti-beam consisting of those secondary electron beams is magnified bythe magnifying lenses 741 and 743, and after having passed through theplurality of apertures 7451 of the second multi-aperture plate 745, eachbeam of the multi-beam is detected by the detector 761. The detectionsignal is sent to the image data processing section 771 of the processcontrol system 77 q via the amplifier 763 to form the secondary electronimage pattern.

The stage unit 50 n moves the wafer W sequentially or continuously by apredetermined width synchronously so as to allow the multi-beam to scanthe overall surface of the wafer to be inspected. At this point of time,in the laser interferometer 94, a laser oscillator 943 oscillates alaser beam. The oscillated laser beam is split into two beams by a halfmirror or a dichroic mirror 945. One of the beams which has passedthrough the half mirror 945 reaches to the movable mirror 941, while theother beam is reflected by a total reflection mirror 944 and reaches tothe reference mirror 946, thus each of two beams being reflected. Thebeam reflected by the movable mirror 941 passes through the half mirror945 and guided to a receiver or a laser interferometer 942, while thebeam reflected by the reference mirror 946 is reflected again by thetotal reflection mirror 944 and the half mirror 945 to be guided to thereceiver 942. Thus, the receiver 942 detects an interference light ofthe reflected beams from the movable mirror 941 and the reference mirror946. The detection signal is sent to the control section 780, where adistance between the movable mirror 941 and the reference mirror 946along the X and Y directions, i.e., an XY coordinate position of the Xand the Y tables of the stage unit 50 n, is calculated based thereon.

The control section 780, based on the XY coordinate position of the Xand the Y tables of the stage unit 50 n, controls the movement of thestage unit 50 n so as to inhibit any area from being left not-scannedwith the multi-beam. In the present embodiment, since the base bodies ofthe laser reflection mirrors 941, 946 have been made of highly rigidSiC, the flatness of the mirror surfaces can be maintained highlyprecisely without increasing the thickness thereof. This enables thehighly precise position control of the stage unit 50 n, thus allowingthe accurate secondary electron beam image to be obtained. Besides, thelaser reflection mirror which has been made thin is space-saving.Further, the movable mirror 941 which has been made lighter in weightcan reduce the load in moving the stage.

Based on the secondary electron beam image pattern formed in the manneras described above, the control section 780 performs, for example, anevaluation of the wafer as follows.

In a defect inspection method by way of the pattern matching applied tothe wafer W, the control section 780 makes a comparative matchingbetween a secondary electron beam reference image for a wafer having nodefect, which has been stored in the memory in advance, and an actuallydetected secondary electron beam image and calculates a similaritytherebetween. For example, if the similarity indicates a value notgreater than a threshold, it is determined that “a defect exists”, andif the similarity indicates a value greater than the threshold, it isdetermined that “no defect exists”. At this stage, the detected imagemay be displayed on the display section 782. This enables an operator toconfirm and evaluate finally on whether or not the wafer is defective.Further, every segmental region within the image may be comparativelymatched to one another so as to automatically detect the segmentalregion having a defect. At this stage, preferably, an enlarged image ofthe defective region should be displayed on the display section 782.

A method for measuring a line width of a pattern formed on a wafer and amethod for measuring a voltage contrast of the pattern may be same asthose described before in conjunction with FIG. 24, and the explanationsthereof will be omitted.

In FIG. 47, if a blanking deflector 731 is arranged so as to deflect theprimary electron beam toward an aperture of the aperture plate 735disposed in the cross over image formation point at a predeterminedcycle and thereby to permit said beam to pass therethrough for a shortperiod and to block it for the rest of the period, which will berepeated, then it will be possible to form a bundle of beams having ashort pulse width. If such a beam having a short pulse width is used tomeasure the potential on the wafer as described above, the deviceoperation can be analyzed with high time resolution. That is, thepresent electron beam apparatus can be used as what is called an EBtester.

Further Alternative Embodiment of Electron Beam Apparatus

FIGS. 48 and 49 show an alternative embodiment of the electronic-opticalapparatus or the electron beam apparatus designated generally byreference numeral 70 r. In FIGS. 48 and 49, the same components as thosein the electron beam apparatus shown in FIG. 43 are designatedrespectively by the same reference numerals and detailed explanations onthe structure and function thereof will be omitted.

The electron beam apparatus according to the present embodiment is sameas the electron beam apparatus shown in FIG. 43 with the exception thata detection system thereof comprises a control unit 775 r similar to themode determining circuit arranged in the electron beam apparatus shownin FIG. 40. Accordingly, the following discussion is directed only tothe part relating to the detecting and scanning.

Each of the detectors 761 outputs an electric signal representing anintensity of an incident secondary electron beam thereto. Each of thoseelectric signals, after having been amplified by each correspondingamplifier 763, is input to an image data processing section 771 of aprocess control system 77 r. The image data processing section 771converts the electric signal supplied from each of the amplifiers 763into an image data. This can be done because the image data processingsection 771 is also supplied with a scanning signal having given to anelectrostatic deflector 733 for deflecting the primary electron beam.Thus, the image data processing section 771 outputs a set of image datafor respective circuit patterns formed on a wafer W all at once.

A plurality of image data output from the image data processing section771 is sequentially stored into a memory 777 r under a control of acomputer 776 r running according to an operational command from aconsole 778 r. The memory 777 r comprises an image memory section foraccumulating the plurality of image data obtained sequentiallycorresponding to the scanning of the circuit pattern in this way, areference pattern database for accumulating reference patterns to beused for comparing with the image data obtained by the scanning andthereby determining whether or not an irregular pattern exists, and adetermining pattern database for accumulating patterns to be used fordetermining killer defects and other patterns to be used for determiningnon-killer defects. With this configuration, the computer 776 r can workout to compare the image data obtained from a certain circuit patternwith that of the reference pattern and to distinguish the killer defectfrom the non-killer defect by using said determining pattern database.

Besides, the computer 776 r has been programmed to control the scanningof the wafer W with the primary electron beam so that the defectinspection apparatus shown in FIG. 49 may be used to execute anevaluation such as a defect inspection of a pattern formed on a surfaceof the wafer W. That is, the computer 776 r controls an electrostaticdeflector 733 and an magnetic deflector 727 of a Wien filter or an ExBseparator 726 to work interlockingly so as to scan the surface of thewafer W in the X direction with a plurality of beams, while controllingthe stage unit 50 n to move the wafer W continuously in the Y direction,thereby accomplishing the scanning of the overall surface of the waferW.

To explain in more specific, after having controlled the stage unit 50 nto move and place the wafer W at a scanning starting end, the computer776 further controls the stage unit to move continuously in theY-direction while controlling a plurality of primary electron beams toscan in the X-direction with an amplitude slightly greater than adistance between respective primary electron beams, Lx (shown in FIG.9). This means that the wafer could have been scanned in the regionextending along the Y-direction having a width w equivalent to fullscanning distance of the plurality of primary electron beams in theX-direction, and a signal in association with the scanning in saidregion would be output from a detector 761.

Subsequently, after the X table of the stage unit 50 n having been movedin the X-direction by a step equivalent to the width w, the Y table ofthe stage unit 50 n is continuously moved in the Y-direction whilecontrolling the plurality of primary electron beams to scan the wafer Win the X-direction by the distance equivalent to the width w. Thereby,another region of the width w adjacent to the region having beenpreviously scanned would have been scanned both in the X- and theY-directions. After this, the similar operations may be repeated thus toscan the overall surface of the wafer W, and the signal obtained as aresult of scanning operations from the detector 761 may be processed soas to evaluate the wafer W.

It is to be noted that a distance measuring operation of the stage unitis same as that in the embodiment described in conjunction with FIG. 43,and the explanation thereof will be omitted.

If the wafer W is a semiconductor wafer, the following method may beemployed to evaluate the wafer W. That is, a marker may be arranged atan appropriate location on the surface of the wafer W, such that onlythe one electron beam among a plurality of primary electron beams, whichhas been formed by one aperture of a multi-aperture plate 723, may beallowed to scan said marker and an output from the detector at that timeof scanning is extracted thus to detect the position of the marker.Thereby a physical relationship between the wafer W and the primaryelectron beam can be determined, and therefore if an arrangement of acircuit pattern formed on the surface of the wafer W with respect to theX- and the Y-directions have been determined in advance, a plurality ofprimary electron beams could be guided to the correct position to meetsaid circuit pattern and the beams therein could scan the circuitpattern, thereby accomplishing the evaluation of the circuit pattern onthe wafer W.

Further, the line width of the pattern on the surface of the wafer W canbe measured in such a way that first a pattern to be evaluated on thewafer W is moved by registration to the proximity to the optical axis ofthe primary optical system and the wafer W is line-scanned with theprimary electron beam to detect the secondary electron beam, and then asignal corresponding to this secondary electron beam is detected toextract a signal for evaluating the line width of the circuit pattern onthe surface of the wafer W, which is then calibrated appropriately thusto measure the line width of the pattern on the surface of the wafer W.

It is to be appreciated that forming an image of each one of thesecondary electron beams on each corresponding one of those apertures ofthe second multi-aperture plates 745 or, in other words, aligning theorbit of the secondary electron beam, Tr2, with each corresponding oneof those apertures of the second multi-aperture plate 745 will bepossible if one piece of lens is arranged downstream to the E×Bseparator 726, which may facilitate said image formation or alignment ofthe secondary electron beam by changing an excitation of the magnifyinglens 743 and shifting the cross over point P3. Although theseadjustments may cause a mismatch in the focusing condition for thesecondary electron beam, if the aperture of the second multi-apertureplate 745 was formed so as to have a larger diameter, then the secondaryelectron detection efficiency would not be deteriorated, and accordinglythe above adjustments would never cause any disadvantages to the defectinspection.

Now, referring to FIGS. 49 [A], [B], and [C], there will be describedhow the computer 776 r in the electron beam apparatus of FIG. 48 worksto distinguish a killer defect from a non-killer defect. As having beendescribed before, as a plurality of semiconductor chips on the wafer Wis scanned all at once with a plurality of electron beams, image datarepresenting the circuit pattern on each of the semiconductor chip isaccumulated one after another in the memory 777 r. Then, the operator,at any appropriate point of time when the memory 777 r has stored theaccumulated image data for some parts or all parts of each circuitpattern, sends a command to the computer 776 r from the console 778 r toexecute a defect inspection operation. The computer 776 r has beenprogrammed to execute in response to said command the operationcomprising the steps of:

(1) reading out a part of the image data for the circuit pattern of oneof the semiconductor chips and the image data for the reference patterncorresponding thereto from the memory 777 r;

(2) making a comparison between said two image data;

(3) as a result of the comparison, identifying a normal pattern and anabnormal pattern and then taking out the image data containing theabnormal pattern;

(4) comparing said taken-out image data with the contents of thedetermining pattern database in the memory 777 r and determining whetherthe abnormal pattern is considered to be the killer defect or thenon-killer defect;

(5) subsequently, executing said steps from (1) to (4) for all otherparts of the image data obtained from the scanning thus to end thedefect inspection of the circuit pattern for the current semiconductorchip; and then

(6) repeating said steps from (1) to (5) for the image data obtainedfrom the scanning for every remaining semiconductor chips one by one,thus to complete the defect inspection for all of the semiconductorchips to be inspected.

Herein, there will now be described an algorithm for determining whetherthe location determined to be the abnormal pattern is the killer defector the non-killer defect. This algorithm is based on such an empiricalrule that “although the obtained image data is representative of theabnormal pattern, it should be considered with a considerably highprobability that said location is actually of a conductive material”.Then, it is assumed that as the result of the scanning of a certaincircuit pattern, three kinds of images as shown in FIGS. 49 [A], [B] and[C] were obtained as the images including the abnormal patterns. In thedrawings, those white rectangular portions Ptn without hatching are theimages representative of the normal patterns and those rectangularportions Pta-1, Pta-2 with hatching are the images representative of theabnormal patterns. Among those rectangular patterns corresponding to theabnormal patterns, the rectangular portion Pta-1 shown in [A] is incontact with a single rectangular portion Ptn, the rectangular portionPta-1 shown in [B] has no contact with any rectangular portions Ptn, andthe rectangular portions Pta-2 shown in [C] are in contact with two ormore rectangular portions Ptn, respectively. Then, based on saidempirical rule, the algorithm determines that the rectangular portionsPta-1 shown in [A] and [B] are the non-killer defects but therectangular portions Pta-2 shown in [C] are the killer defects.

With respect to an image of a contact hole layer, the computer 776 rworks according to said algorithm to determine that an abnormal patternoverlapping with the contact hole is a killer defect and an abnormalpattern having no contact with the contact hole is a non-killer defect.Besides, with respect to an image of a gate layer, the computer 776 rworks to determine such that an abnormal pattern located within thepredetermined range proximal to the gate pattern is indicative of akiller defect and therefore the abnormal pattern located away from thegate pattern by a predetermined distance or much farther is a non-killerdefect.

It is to be appreciated that the determining pattern database within thememory 777 r may be updated by adding a newly found abnormal pattern ateach time when the new abnormal pattern is found so as to be determinedon whether it is the killer defect or the non-killer defect during thecomputer 776 r being operative for the defect inspection.

Further Alternative Embodiment of Electron Beam Apparatus

FIGS. 50 to 52 show an alternative embodiment of the electronic opticalapparatus or the electron beam apparatus designated generally byreference numeral 70 s. In FIGS. 50 to 52, the same components as thosein the electron beam apparatus shown in FIG. 8 are designatedrespectively by the same reference numerals and detailed explanations onthe structure and function thereof will be omitted.

In FIG. 50, an electron gun for emitting an electron beam is designatedby reference numeral 71 s, a primary optical system by 72 s, amulti-aperture plate provided with a plurality of small apertures by 723s, a lens by 721 s, electromagnetic deflectors by 731 s and 733 s, anExB separator by 726 s, an objective lens by 729 s, a secondary opticalsystem by 74 s, lenses by 741 s and 743 s, and a detector for detectinga secondary electron beam by 761 s. Reference numeral 771 s designatesan image forming unit of a process control system 77 s, and 779 sdesignates a scanning control unit, which functions to supply thedeflectors 731 s and 733 s with scanning signals for scanning theelectron beam. The multi-aperture plate 723 s may be provided with, forexample, nine apertures (3×3) as shown in FIG. 51 [A] or seven apertures(1×7) as shown in FIG. 51 [B]. It is to be appreciated that thearrangement and the number of those apertures are not limited to thoseillustrated in FIG. 51, but any aperture pattern may be arbitrarilyemployed if appropriate.

In the apparatus shown in FIG. 50, an electron beam emitted from theelectron gun 71 s is formed into a plurality of beams by a plurality ofapertures of the aperture plate 723 s, and these beams are formed intoimages on a surface of a wafer W through the lenses 721 s and 729 s,while simultaneously the plurality of electron beam is controlled by thedeflectors 731 s and 733 s so as to scan the surface of the wafer W.Under the condition where a stage holding the wafer W has been fixed,the scanning control unit 779 s controls the deflectors 731 s and 733 sto cause the electron beams to scan in the X-axis and the Y-axisdirections. Thereby, with the wafer W being fixed, between those spotshaving formed on the wafer surface at the point of time t₀, other spotsare sequentially formed at the points of time t₁, t₂, . . . , and inthis way, eventually the electron beam spots are formed at all of thepoints within a predetermined area on the surface of the wafer W. Then,the stage with the wafer W loaded thereon is moved, and another areaadjacent to the previously scanned area is similarly scanned.

A secondary electron beam emitted by forming an image of the electronbeam on the wafer W is deflected by the E×B separator 726 s, anddetected by the detector 761 s through the lenses 741 s and 743 s of thesecondary optical system, where the detected beam is converted into anelectric signal and is supplied as a detector output signal to the imageforming unit 771 s.

In the apparatus shown in FIG. 50, for example, the multi-aperture plate723 s provided with nine apertures as shown in FIG. 51 [A] is used toform nine electron beam spots on the surface of the wafer, andaccordingly the detector 761 s is provided with nine detecting elementscorresponding to the array of the apertures of the multi-aperture plate723 s so as to detect the secondary electron beams from those nine spotsrespectively.

The image forming unit 771 s is also supplied with the scanning signalfrom the scanning control unit 779 s, and the detector output signal isassociated with the scanning signal and stored in an image data memory(not shown) as a signal representative of a pixel position. With thissignal, the image forming unit 771 s can form a surface image of thewafer W.

The image representing the wafer surface which has been formed in such amanner as described above is compared in a mismatch/match detecting unit(not shown) as per pixel with a reference image pattern or an imagepattern with no defect stored in advance, and if any mismatching pixelis found out, then it may be determined that the wafer has a defect.Further, the image representing the wafer surface may be displayed onthe monitor screen, and in that case an experienced operator or the likemay monitor the image to inspect the wafer surface for any defects.

Still further, upon measuring a line width of a wiring pattern or anelectrode pattern formed on a wafer, a pattern area to be evaluated ismoved to a location on or near to an optical axis and said area isline-scanned to take out an electric signal to be used for evaluatingthe line width, and then the signal is calibrated as needed thereby todetect the line width.

With an evaluation apparatus having such a structure as above, thepresent invention has suggested a method for inspecting the wafersurface which has been processed by a processing apparatus, in which theevaluation apparatus is arranged in the proximity to the processingapparatus and further a controller (not shown) controls an overalloperation of the evaluation apparatus to inspect only a regionconsisting of a predetermined location or a plurality of predeterminedareas on the wafer surface so that an inspection time for a wafer may bemade approximately equal to a processing time per wafer of saidprocessing apparatus. In this control, at first the wafer is securedonto the stage of the evaluation apparatus, and then minimal requiredevaluation parameter of a wafer and a processing time required per waferare input into the controller of the evaluation apparatus. Theevaluation parameter may be, for example, a fluctuation of a minimumline width in the case of the processing apparatus being a lithographyapparatus, and a defect inspection in the case of the processingapparatus being an etching apparatus. Subsequently, the controllerdetermines an evaluation area or a region to be inspected on the waferbased on the entered evaluation parameter and the entered necessaryprocessing time so that the time required per wafer for evaluating aprocessed condition of the wafer may be made within or approximatelyequal to the processing time required per wafer.

Since the inspection is only applied to the predetermined area andinevitably the range of movement of the wafer W within the evaluationapparatus should be made smaller, therefore a foot print of theevaluation apparatus can be reduced in comparison with the case wherethe inspection is applied to the entire area on the wafer. Further,since the evaluation time has been made approximately equal to theprocessing time, and accordingly the throughput of the evaluationapparatus is also approximately equal to that of the processingapparatus, therefore if any defect is found out, it will be more easierto find out any irregular operation in the processing apparatuscorresponding to the defective condition.

It is to be appreciated that the inspection apparatus may comprise aplurality of optical column units arranged in an array as shown in FIG.52, each unit of the optical column including the electron beamapparatus shown in FIG. 50. That is, FIG. 52 [A] schematically shows anarray of the electron beam spots on the wafer W in the case of sixoptical columns arranged in the array of 2 rows×3 columns, eachincluding the multi-aperture plate 723 s with nine apertures as shown inFIG. 51[A]. On the other hand, FIG. 52 [B] schematically shows an arrayof the electron beam spots on the wafer W in the case of four opticalcolumns arranged in line, each including the multi-aperture plate 723 swith seven apertures arranged in line as shown in FIG. 51[B].

In FIG. 52, a group of beam spots generated by each of the opticalcolumns is indicated by a circle designated with the reference BG, and astraight line R extending from the center of each circle indicates thedirection of the emission of the secondary electron beam in each of theoptical columns, that is, the orientation of the secondary electron beamdetection system comprising the lenses 741 s and 743 s and the detector761 s. As shown in FIGS. 52 [A] and [B], the secondary electron beamdetection systems have been arranged so as not to interfere with oneanother, and with such arrangement, a plurality of optical columns maybe installed in the efficient manner thus to prevent the foot print forthe entire evaluation apparatus from being oversized.

It is to be noted that the arrangement and the number of the pluralityof optical columns, as a matter of course, are not limited to thoseshown in FIGS. 52 [A] and [B]. In the case where the optical columns inthe array of 1×N as shown in FIG. 52 [B] is employed, the wafer W may bemoved continuously in the direction indicated by the arrow “a”, ifappropriate.

Also, in the second embodiment using a plurality of optical systems,similarly to the first embodiment, the evaluation apparatus may beplaced in the proximal to the processing apparatus and furthermore thecontrol system (not shown) may control the operation thereof such thatthe inspection time for a wafer can be made approximately equal to theprocessing time per wafer of said processing apparatus. In that case,the wafer may be inspected with a full-face inspection or with a partialinspection limited to a predetermined region on the wafer surfacedepending on the processing time, and the important point is that theinspection operation would be controlled such that the processing timeper wafer should be approximately matched to the inspection time perwafer. In this case also, the range necessary for moving the wafer canbe made smaller, and thereby the foot print for the evaluation apparatuscan be reduced. Besides, since the throughput of the evaluationapparatus is made approximately equal to the throughput of theprocessing apparatus, if a defect is found out, it will be much easierto find out an irregular operation in the processing apparatus.

Further, upon evaluating a processed condition in a processing apparatuswith an especially shorter processing time, a sampling inspection on thebasis of one for every two wafers or one for every three wafers may beemployed so as to make a better matching between the throughputs perlot.

Further Alternative Embodiment of Electron Beam Apparatus

Now, referring to FIGS. 53 to 59, a defect inspection of a patternformed on a wafer will be described in detail. It is to be noted that inFIG. 53, an embodiment in which an inspection apparatus is applied towhat is called an electron beam apparatus of the multi-beam type isdesignated generally by a reference numeral 70 t, and componentscorresponding to those in the preceding embodiments are designated bythe same reference numerals, each added with a suffix “t”, whereinexplanations of the structure and function of those components will beomitted and only the contents which have been newly added may beexplained in detail.

In FIG. 53, the reference numeral 71 t denotes an electron gun foremitting a primary electron beam, 721 t denotes an electrostatic lensfor converging the emitted primary electron beam, 726 t denotes an E×Bdeflector which allows the appropriately shaped primary electron beam toadvance straight in the field consisting of an electric field and amagnetic field crossing orthogonally with each other so as to impingeupon a semiconductor wafer W at an approximately right angle, 729 tdenotes an objective lens for forming the deflected primary electronbeam into an image on the wafer W, 50 t denotes a stage unit capable ofmoving within a horizontal plane with the wafer W loaded thereon, 741 tdenotes an electrostatic lens for forming a secondary electron beamemitted from the wafer W by the irradiation of the primary electron beaminto an image, and 761 t denotes a detector for detecting individuallyan intensity of each beam for each of the formed images. A signal fromthe detector 761 t is input into an image forming circuit 765 t thus toform a secondary electron image. The electron beam apparatus in thisembodiment further comprises a process control system 77 t for executingan operation for detecting a defect on the wafer W based on thesecondary electron image detected by the detector 761 t whilecontrolling the whole apparatus. It is to be appreciated that althoughan image by scattered electrons or reflected electrons may be obtainedas said secondary electron image other than the image by the secondaryelectrons, herein, the case where the obtainment of the secondaryelectron image is selected will be described exclusively.

Further, a deflecting electrode 733 t is interposed between an objectivelens 729 t and the wafer W for deflecting an angle of incidence of theprimary electron beam to the wafer W by the electric field or the like.This deflecting electrode 733 t is connected with a deflectioncontroller 75 t for controlling an electric field of said deflectingelectrode 733 t. This deflection controller 75 t is connected to theprocess control system 77 t and controls said deflecting electrode 733 tso that the deflecting electrode 733 t can generate the electric fieldin response to a command from the process control system 77 t. It is tobe noted that the deflection controller 75 t may be implemented as avoltage controller for controlling a voltage to be applied to thedeflecting electrode 733 t.

The detector 761 t may have any arbitrary structure so far as it canconvert the secondary electron image formed by the electrostatic lens741 t into a signal, which can be processed in a subsequent stage.

The process control system 77 t may be constituted of a general-purposepersonal computer and the like as shown in FIG. 53. This computer maycomprise a control section main body 791 for executing a variety ofcontrols and arithmetic processing according to a predetermined program,a CRT 796 for indicating a processing result of the main body 791 and aninput section 797 such as a key board or a mouse for enabling anoperator to input a command. As a matter of course, the process controlsystem 77 t may be constituted of a hardware dedicated to a defectinspection apparatus or a workstation.

The control section main body 791 comprises a variety of control boards,including a CPU, a RAM, a ROM, a hard disk, and a video board. Asecondary electron image memory area 792 has been allocated on a memorysuch as the RAM or the hard disk for storing the electric signalreceived from the detector 761 t, i.e., the digital image data of thesecondary electron image for the wafer W. Further, on the hard disk,there is a reference image memory section 793 for storing beforehand areference image data for the wafer having no defect. Still further, onthe hard disk, in addition to the control program for controlling thewhole unit of the defect inspection apparatus, a defect detectionprogram 794 is stored for reading the secondary electron image data fromthe memory area 792 and automatically detecting a defect in the wafer Wbased on said image data according to the predetermined algorithm. Thisdefect detection program 794, as will be described in more detail later,has such a function that it performs a matching of reference image readout from the reference image memory section 793 to an actually detectedsecondary electron image in order to automatically detect any defectiveparts, so that it may indicate a warning to the operator when itdetermines there is the defect existing. In this regard, the CRT 796 maybe designed to display the secondary electron image EIm on the displaysection thereof.

An operation of the defect inspection apparatus according to the firstembodiment will now be described by taking flow charts of FIGS. 55 to 57as examples.

First of all, as shown in the flow of the main routine of FIG. 55, thewafer W to be inspected is placed on the stage 50 t (step 1000). Thisstep may be performed in the mode that the loader automatically sets thewafers W one after another onto the stage unit 50 t as explained above.

Then, images for a plurality of regions to be inspected are respectivelyobtained, which are displaced one from another while being superimposedpartially one on another on the XY plane of the surface of the wafer W(Step 1002). Each of said plurality of regions to be inspected, fromwhich the image is to be obtained, is, for example, a rectangular regionon the wafer surface TS to be inspected as designated by referencenumerals RA1, RA2, . . . , Rak, . . . in FIG. 59, each of which isobserved to be displaced relative to one another while being partiallysuperimposed one on another around the inspection pattern TPt of thewafer. For example, 16 pieces of images TAI for the regions to beinspected (the images to be inspected) may be obtained as shown in FIG.54. Herein, for the image shown in FIG. 54, each segment of rectangularshape corresponds to one pixel (or a block, whose unit is greater thanthe unit of pixel), and among those segments, shaded ones correspond tothe imaged area of the pattern on the wafer W. This step 1002 will bedescribed in more detail later with reference to the flow chart of FIG.56.

Then, the image data for the plurality of regions to be inspected, whichhave been obtained at Step 1002, are compared respectively with thereference image stored in the memory section 793 to look for anymatching (Step 1004 in FIG. 55), and it is determined whether or notthere is a defect existing in the wafer inspection surface encompassedby said plurality of regions to be inspected. This process performs,what is called, the matching operation between image data, which will beexplained later in detail with reference to the flow chart shown in FIG.57.

If the result from the comparing process at Step 1004 indicates thatthere is a defect in the wafer inspection surface encompassed by saidplurality of regions to be inspected (Step 1006, affirmativedetermination), the process gives a warning to the operator indicatingthe existence of the defect (Step 1008). As for the way of warning, forexample, the display section of the CRT 796 may display a messagenotifying the operator that there is a defect, or at the same time mayadditionally display a magnified secondary electron image EIm of thepattern determined to have the defect. Such defective wafers may beimmediately taken out of the stage device to be stored in anotherstorage separately from those wafers having no defect (Step 1010).

If the result from the comparing process at Step 1004 indicates thatthere is no defect in the wafer W (Step 1006, negative determination),it is determined whether or not there are remained more regions to beinspected for the wafer W currently treated as the inspection object(Step 1012). If there are more regions remained for inspection (Step1012, affirmative determination), the stage device 50 t is driven tomove the wafer W so that other regions to be further inspected arepositioned within the irradiating region of the primary electron beam(Step 1014). Subsequently, the process goes back to Step 1002 to repeatthe similar operations for said other regions to be inspected.

If there is no more regions remained to be further inspected (Step 1012,negative determination), or after a drawing out processing of thedefective wafer (Step 1010), it is determined whether or not the currentwafer treated as the inspection object is the last wafer to beinspected, that is, whether or not there are any wafers remaining forthe inspection in the loader, though not shown (Step 1016). If thecurrent wafer is not the last one (Step 1016, negative determination),the wafers having been inspected already are stored in a predeterminedstoring location, and a new wafer which has not been inspected yet isset instead on the stage device (Step 1018). Then, the process goes backto Step 1002 to repeat the similar operations for said wafer. Incontrast, the current wafer is the last one (Step 1016, affirmativedetermination), the wafer having been inspected is stored in thepredetermined storing location to end the whole process.

Then, the process flow of the step 1002 will now be described withreference to the flow chart of FIG. 56.

In FIG. 56, first of all, an image number “i” is set to the initialvalue “1” (Step 1020). This image number is an identification numberassigned serially to each of the plurality of images for the regions tobe inspected. Secondary, an image position (X_(i), Y_(i)) is determinedfor the region to be inspected as designated by the set image number i(Step 1022). This image position is defined as a specific locationwithin the region to be inspected for bounding said region, for example,a central location within said region. Currently, i=1 defines the imageposition as (X₁, Y₁), which corresponds, for example, to a centrallocation of the region to be inspected RA1 as shown in FIG. 59. Theimage position has been determined previously for every image region tobe inspected, and stored, for example, in the hard disk of the processcontrol system 77 t to be read out at Step 1022.

Then, the deflection controller 75 t applies a potential to thedeflecting electrode 733 t (Step 1024 in FIG. 56) so that the primaryelectron beam passing through the deflecting electrode 733 t of FIG. 53may be irradiated onto the image region to be inspected in the imageposition (X_(i), Y_(i)) having determined at Step 1022.

Then, the electron gun 71 t emits the primary electron beam, which goesthrough the electrostatic lens 721 t, the ExB separator 726 t, theobjective lens 729 t and the deflecting electrode 733 t, and eventuallyimpinges upon a surface of the set wafer W (Step 1026). At that time,the primary electron beam is irradiated onto the image region to beinspected at the image position (X_(i), Y_(i)) on the wafer inspectionsurface TS. When the image number i=1, the region to be inspected isRA1.

Secondary electrons are emitted from the region to be inspected, onwhich the primary electron beam has been irradiated. Then, the generatedsecondary electron beam is formed into an image on the detector 761 twith a predetermined magnification by the electrostatic lens 741 t ofthe magnified projection system. The detector 761 t detects the imagedsecondary electron beam, and converts it into an electric signal or adigital image data for each detecting element and outputs this signal(Step 1028). Then, the detected digital image data for the image numberi is transmitted to the secondary electron image memory area 792 (Step1030).

Subsequently, the image number i is incremented by 1 (Step 1032), and itis determined whether or not the incremented image number (i+1) isgreater than a constant value “i_(MAX)” (Step 1034). This i_(MAX) is thenumber of images to be obtained for inspection, which is “16” for theabove example of FIG. 54.

If the image number i is not greater than the constant value i_(MAX)(Step 1034, negative determination), the process goes back to Step 1022again, and determines again the image position (X_(i+1), Y_(i+1)) forthe incremented image number (i+1). This image position is a positionshifted from the image position (X_(i), Y_(i)) having determined in theprevious routine by a specified distance (ΔX_(i), ΔY_(i)) in theX-direction and/or the Y-direction. The region to be inspected in theexample of FIG. 59 is at the location (X₂, Y₂) i.e., the rectangularregion RA2 indicated with the dotted line, which has been shifted fromthe position (X₁, Y₁) only in the Y-direction. It is to be noted thatthe value for (ΔX_(i), ΔY_(i)) (i=1,2, . . . i_(MAX)) may have beendetermined appropriately from the data indicating practically andexperimentally how much is the displacement of the pattern TPt on thewafer inspection surface TS from the field of view of the detector 761 tand the number and the area of the regions to be inspected.

Then, the operations for Step 1022 to Step 1032 are repeated for i_(MAX)pieces of region to be inspected. These regions to be inspected arecontinuously displaced while being partially superimposed one on anotheron the wafer inspection surface TS so that the image position after ktimes of shifting (X_(k), Y_(k)) corresponds to the inspection imageregion RAk, as shown in FIG. 59. In this way, the 16 pieces ofinspection image data exemplarily illustrated in FIG. 54 are obtainedinto the image memory area 792. It is observed that a plurality ofimages TAI obtained for the regions to be inspected (i.e., inspectionimages) contains partially or fully the image Ipt of the pattern TPt onthe wafer inspection surface TA, as illustrated in FIG. 54.

If the incremented image number i has become greater than i_(MAX) (Step1034, affirmative determination), the process returns out of thissubroutine and goes to the comparing process (Step 1004) in the mainroutine of FIG. 55.

It is to be noted that the image data that has been transferred to thememory at Step 1030 is composed of intensity values of the secondaryelectrons for each pixel (so-called, raw data) detected by the detector761 t, and these data may be stored in the memory area 792 after havingbeen processed through various operations in order to use for performingthe matching operation relative to the reference image in the subsequentcomparing process (Step 1004 of FIG. 55). Such operations includes, forexample, a normalizing process for setting a size and/or a density ofthe image data to be matched with the size and/or the density of thereference image data, or the process for eliminating as a noise theisolated group of elements having the pixels not greater than thespecified number. Further, the image data may be converted by means ofdata compression into a feature matrix having extracted features of thedetected pattern rather than the simple raw data, so far as it has notnegatively affect on the accuracy in detection of the highly precisepattern. Such feature matrix includes, for example, m×n feature matrix,in which a two-dimensional inspection region composed of M×N pixels isdivided into m×n (m<M, n<N) blocks, and respective sums of intensityvalues of the secondary electrons of the pixels contained in each block(or the normalized value defined by dividing said respective sums by atotal number of pixels covering all of the regions to be inspected)should be employed as respective components of the matrix. In this case,the reference image data also should have been stored in the same formof representation. The image data in the context used in the embodimentsof the present invention includes, of course, not only a simple raw databut also any image data having the feature extracted by any arbitraryalgorithms as described above.

The process flow for Step 1004 will now be described with reference tothe flow chart of FIG. 57.

First of all, the CPU in the process control system 77 t reads thereference image data out of the reference image memory section 793 (FIG.53) onto the working memory such as the RAM or the like (Step 1040).This reference image is identified by reference numeral SIm in FIG. 54.Then, the image number “i” is reset to 1 (Step 1042), and then theinspection image data for the image number i is reads out onto theworking memory (Step 1044).

Then, the read out reference image data is compared with the data of theimage “i” for any matching to calculate a distance value “D_(i)” betweenboth data (Step 1046). This distance value D_(i) indicates a similaritylevel between the reference image and the image to be inspected “i”,wherein a greater distance value indicates the greater differencebetween the reference image and the inspection image. Any unit of amountmay be used for said distance value D_(i) so far as it may represent thesimilarity level. For example, if the image data is composed of M×Npixels, the secondary electron intensity (or the amount representativeof the feature) of each pixel may be considered as each of the positionvector elements of M×N dimensional space, so that an Euclidean distanceor a correlation coefficient between the reference image vector and theimage “i” vector in the M×N dimensional space may be calculated. It willbe easily appreciated that any distance other than the Euclideandistance, for example, the urban area distance may be calculated.Further, if the number of pixels is huge, which increases the amount ofthe operation significantly, then the distance value between both imagedata represented by the m×n feature vector may be calculated asdescribed above.

Subsequently, it is determined if the calculated distance value D_(i) issmaller than a predetermined threshold Th (Step 1048). This threshold This determined experimentally as a criterion for judging a sufficientmatching between the reference image and the image to be inspected. Ifthe distance value D_(i) is smaller than the predetermined threshold Th(Step 1048, affirmative determination), the process determines that theinspection plane TS of the wafer W has “no defect” (Step 1050) andreturns out of this sub routine. That is, if there has been found atleast one image among those inspection images matching to the referenceimage, the process determines there is “no defect”. Accordingly, sincethe matching operation shall not necessarily be applied to everyinspection image, the high-speed judgment becomes possible. As for theexample of FIG. 54, it is observed that the image to be inspected at thecolumn 3 of the row 3 is approximately matching to the reference imagewithout any offset thereto.

When the distance value D_(i) is equal to or greater than the thresholdTh (Step 1048, negative determination), the image number “i” isincremented by 1 (Step 1052), and then it is determined whether or notthe incremented image number (i+1) is greater than the predeterminedvalue i_(MAX) (Step 1054).

If the image number “i” is not greater than the predetermined valuei_(MAX) (Step 1054, negative determination), the process goes back toStep 1054 again, reads out the image data for the incremented imagenumber (i+1), and repeats the similar operations.

If the image number “i” is greater than the predetermined value i_(MAX)(Step 1054, affirmative determination), then the process determines thatsaid inspection plane TS of the wafer W has “a defect existing” (Step1056), and returns out of the sub routine. That is, if any one of theimages to be inspected is not approximately matching to the referenceimage, the process determined that there is “a defect existing”.

Although in the above embodiment, the inspection method has beendescribed in conjunction with the electron beam apparatus of themulti-beam type, one selected from a variety of types, the inspectionmethod according to this embodiment is also applicable to, for example,an electron beam apparatus of the scanning type as illustrated in FIG.45. However, herein, an illustration of such electron beam apparatusshould be omitted for the simplicity.

It is to be appreciated that although in the above description for theembodiment, each of the electron beam apparatuses having individually acharacteristic portion has been distinctively explained, a singleelectron beam apparatus may include a plurality of characteristicportions described above in combination.

Effect of the Invention

According to a method for inspecting a substrate, a substrate inspectionapparatus and a charged particle beam apparatus to be used in saidsubstrate inspection apparatus, the following effect may be broughtabout.

(1) Since the electron beam consisting of a plurality of primary chargedparticle beams is irradiated onto and thereby to scan the sample all atonce so as to obtain a plurality of sub-image data, and said sub-imagedata are rearranged based on the consideration of the X-Y coordinatesthereof and then synthesized so as to obtain the image data for theregion to be inspected on the wafer, throughput of the apparatus can beincreased distinctively.

(2) Since the electron gun for emitting the charged particle beam hasbeen designed so as to be operated in the space charge limited region,the S/N ratio can be increased to a great degree as compared with thecase where the electron gun is operated in the temperature limitedregion according to the prior art. Accordingly, the S/N ratio ofequivalent level to that having accomplished by the prior art can beobtained with lower beam current.

(3) Since even if a plurality of primary electron beams are used to scanthe sample wafer all at once, the S/N ratio of a predetermined level canbe obtained with still lower beam current, therefore a blur of the beamdue to the space charge effect can be reduced to negligibly low level.

(4) Since the electron beam apparatus can be operated by quicklyselecting either of a mode allowing for a precise evaluation yet with asmall throughput or another mode allowing for a rough evaluation stillwith a large throughput, the efficient inspection or evaluation of thesample can be accomplished.

(5) Since the electrostatic lens is made by machining a single block ofinsulating material, and thereby the high precision lens of smallerdiameter can be produced, the electron beam apparatus can be madecompact and a plurality of optical columns can be arranged collectivelyfor the wafer having a large diameter thus to accomplish an inspectionand/or evaluation with high throughput.

(6) Since the circuit pattern formed on a surface of the sample iscaptured as the rectangular pattern information rather than the 0 and 1binary information, it will become possible to improve a capacity of amemory for accumulating said image patterns, a rate of data transmissionand a rate of data comparison to a great degree (this effect may appearsignificant specifically in a layer of lower pattern density such as acontact hole layer or a gate layer).

(7) Since at least one step of lens is used to magnify the secondaryelectron image, the focusing condition and/or the magnification for thesecondary optical system is made adjustable separately from theadjustment of the lens condition for the primary optical system,therefore any offsets from those design values can be compensated andalso any detected defects can be classified so as to detect a criticaldefect accurately and quickly.

(8) Since in the semiconductor manufacturing process, the inspection canbe applied intensively only to a region where the defect is apt tooccur, the inspection time can be shortened and substantially all thedefects required to be detected can be accordingly detected.

(9) Since the bulk material of highly rigid SiC ceramic has beenemployed for the laser reflection mirror to be used in the laserinterferometer, a distortion or a bowing of the mirror surface can beeliminated thus to improve a precision of flatness thereof withoutthickening the base body and also an erroneous detection in the positionmeasurement can be prevented, and in addition, the weight of the stageas well as a space necessary for moving the stage can be reduced.

Further, since the laser reflection mirror according to the presentinvention is made in such a manner that the SiC ceramic base body istreated with a SiC film deposition to be covered therewith and then ispolished to be a mirror-surface, therefore such an advantageous effectcan be provided in that there is no fear of film stripping due to theaging. Still further, in the film deposition of SiC, if the SiC isdeposited from various directions diagonal with respect to the surfaceof the base body, then a concave problem in the mirror surface caused bya void can be appropriately dissolved thus to maintain the high level offlatness on the mirror surface.

Further, since a portion common to the primary and the secondary opticalsystems has been minimized while satisfying the requirement, in additionto the effects described above, there has been provided anotheradvantage that the primary and the secondary optical systems can beadjusted almost independently, and in that case, a cross talk betweenelectron beams can be eliminated by making a spacing between the primaryelectron beams greater than a resolution of the secondary optical systemas converted into a surface of the sample.

(10) Since a single electron optical column has been provided with atleast one step of axially symmetric lens which is made by machining ablock of ceramic and selectively applying a metal coating onto a surfacethereof so as to accomplish a reduced outer diameter, in addition to theeffects described above, there has been provided another advantage thata plurality of electronic-optical optical columns can be arranged inparallel over one piece of sample thus to improve the throughput of theinspection or evaluation of the sample.

(11) Further, according to the device manufacturing method of thepresent invention, since the above-described electron beam apparatus canbe used to evaluate the wafer during being processed or after havingbeen processed with high throughput as well as with high level ofaccuracy, such advantageous effects can be obtained that a yield of theproduct is improved and the delivery of any defective products isprevented.

(12) Since a killer defect and a non-killer defect can be distinguishedfrom each other automatically even for a region having a minimum linewidth of not greater than 0.1 micron, it will become possible to providea highly reliable defect inspection.

(13) Since a new pattern for either of a killer defect and a non-killerdefect can be added into a database at each time when it has been foundduring a defect inspection period, it will become possible to provide auser friendly apparatus.

(14) Since the image data obtained from the adjacent secondary electronbeams can be used to detect a mismatching portion and/or a defect, itwill become possible to reduce a memory capacity for accumulating theimage data.

(15) Since at least the outer side of the electrostatic lens to be usedas the objective lens has been made of ceramic material having a lowcoefficient of linear expansion and further the stationary laser mirroris attached to this ceramic material or the ceramic material itself hasbeen mirror-finished to form the stationary laser mirror, therefore itwill be possible to provide an accurate evaluation of the sample even inthe circumstance of low stability in temperature or in the case ofrelative vibration occurring between the optical system and the samplechamber.

(16) Since a single unit of apparatus can perform a multi-purposeinspection, measurement and evaluation including a defect inspection, adefect reviewing, a pattern line width measurement, and a patternpotential measurement, such a problem can be prevented that a large footprint in a clean room has been occupied by the inspection apparatus, andas a result, a larger number of device manufacturing apparatuses isallowed to be arranged therein, thereby providing an efficient way forusing the clean room.

Further, with a plurality of optical columns to be arranged and amulti-beam for irradiating the sample surface and correspondingly aplurality of detecting elements to be arranged for each of the opticalcolumns, a throughput of the inspection process (a volume of inspectionper unit time) can be increased.

(17) Since the electron beam apparatus and the inspection apparatus canbe made compact and at the same time a throughput of the electron beamapparatus can be matched with a throughput of the processing apparatusof the wafer, and thereby an operation in the processing apparatus canbe checked at real time when the wafer containing the defect isdetected, such a fear can be reduced that the wafers containing defectsmight be undesirably fabricated continuously.

(18) Since the stage can exhibit a highly precise positioning abilitywithin the vacuum atmosphere and further the pressure in the chargedparticle beam irradiating location is hardly increased, the processingwith the charged particle beam against the sample can be performed withhigh level of accuracy.

(19) The gas which has been desorbed from the hydrostatic bearingsupport section is almost completely blocked by the divider and therebyit hardly run over the divider to reach onto the charged particle beamirradiating region side. This can help further stabilize a vacuum levelin the charged particle beam irradiating location.

(20) Since an inspection apparatus can be provided, in which the stagehas a highly accurate positioning function and a vacuum level in thecharged particle beam irradiating region is stable, it will be possibleto provide the inspection apparatus with higher inspection performanceand without any fear of contamination to the sample.

(21) Since such an exposing apparatus can be provided, in which thestage has a highly accurate positioning function and a vacuum level inthe charged particle beam irradiating region is stable, it will bepossible to provide the exposing apparatus with higher exposing accuracyand without any fear of contamination to the sample.

(22) The stage having a similar configuration to the stage of thehydrostatic bearing type which has been typically used in the atmosphere(a stage supported by the hydrostatic bearing having no differentialpumping mechanism) can be used to provide a stable processing by thecharged particle beam against a sample on the stage.

(23) Since it has become possible to minimize the affection to thevacuum level in the charged particle beam irradiating region, theprocessing by the charged particle beam against the sample can bestabilized.

(24) It has become possible to provide at a low price the exposingapparatus in which the stage has a highly accurate positioning functionand a vacuum level in the charged particle beam irradiating region isstable.

(25) Since the present invention allows a plurality of images to betaken for a plurality of regions to be inspected each displaced fromothers while partially superimposing with each other on the sample andalso allows each of these images subject to the inspection to becompared with the reference image thus to detect a defect in the sample,therefore such an advantageous effect can be obtained that adeterioration in the defect detecting accuracy due to the positionmismatch between the image subject to the inspection and the referenceimage is prevented.

(26) Since the present invention allows the above-described chargedparticle beam apparatus to be used to evaluate the wafer during beingprocessed or after having been processed, such an advantageous effecthas been obtained that the highly accurate evaluation may beaccomplished, a yield in the device manufacturing process may beimproved and any defective products can be prevented from beingdelivered.

1. A substrate inspection method comprising: emitting a primary chargedparticle beam from a charged particle beam source, wherein said chargedparticle beam source is actuated in a space charge limited region,wherein a shot noise reduction factor is smaller than 1 and said chargeparticle beam source has a pointed cathode; focusing said emittingcharged particle beams into a fine beam; irradiating and scanning saidfine charged particle beam onto a substrate through a primary opticalsystem; introducing a secondary charged particle beam into a secondarycharge particle beam detector, said secondary charged particle beambeing emitted from said substrate by said irradiation of said primarycharged particle beam; detecting said secondary charged particle beamhaving been introduced into said secondary charge particle beam detectorand converting said detected secondary charged particle beam into anelectric signal; and processing said electric signal to evaluate saidsubstrate, wherein said shot noise reduction factor is defined by thefollowing equation,S/N=n ^(1/2)/(Γ*2^(1/2)) where, S/N is signal to noise ratio, Γ is shotnoise reduction factor, and n is the number of detected secondaryelectrons per pixel.
 2. A substrate inspection method according to claim1, wherein the primary charged particle beam emitted from said chargedparticle beam source is irradiated onto a multi aperture plate having aplurality of apertures, and a plurality of charged particle beams havingpassed through said plurality of apertures are irradiated onto asubstrate surface.
 3. A substrate inspection method according to claim1, further comprising: detecting the secondary charged particle beamemitted from said substrate to obtain image data; and re-arranging saidobtained image data to generate image data of an inspection region onthe substrate.
 4. A substrate inspection method according to claim 1,further comprising: storing in advance reference image data with respectto the substrate to be evaluated; and evaluating the substrate bycomparing said image data generated by an image source with said storedreference image data.
 5. A substrate inspection method according toclaim 2, further comprising: obtaining respective sub-image data bydetecting said secondary charged particle beam emitted from a pluralityof beams of said substrate; wherein said substrate is controlled so ascontinuously move in the Y-axis direction, respective charged particlebeams are driven to simultaneously scan in the X-axis direction suchthat a scanning pitch of a plurality of primary charged particle beamson said substrate are arranged with equal spacing therebetween.
 6. Asubstrate inspection method according to claim 1, wherein a lenscondition or an axial alignment condition of said primary and saidsecondary optical systems corresponding to a pixel size for scanning andirradiating said substrate are stored.
 7. A substrate inspection method,according to claim 1, further comprising: converting said electricsignal into a pattern information; and comparing said patterninformation with a reference pattern.
 8. A substrate inspection methodaccording to claim 1, further comprising: converting said electricsignal received from said detection section into binary information;converting said binary information into a rectangular patterninformation; and comparing said rectangular information with a referencepattern.
 9. A substrate inspection method according to claim 1, furthercomprising: storing a reference image corresponding to said image ofsaid substrate; reading out said stored reference image; comparing saidimage of said substrate with said readout reference image and detectingportions differing between each of said images; and classifying saiddifferent portions into such defects including at least short-circuit,disconnection, convex, chipping, pinhole and isolation.